Add subgroup filtering to xs view

app/assets/javascripts/activities.coffee

   clipboard = new Clipboard('.copy-reactions', {
     'text': clipreactions
   })
-  $('#subgroup_filter').on('change', (e) -> filterparticipants(e))
+  $('.subgroup-filter').on('change', (e) -> filterparticipants(e))
 
 @clipreactions = (trigger) ->
   id = trigger.dataset['activity']

app/views/activities/show.html.haml

         = t 'activities.participant.plural'
         = render partial: "state_counts", locals: {counts: @counts}
     .col-md-6
-      = select_tag(:subgroup_filter, options_for_select(@subgroup_ids), class: 'form-control')
+      = select_tag(:subgroup_filter, options_for_select(@subgroup_ids), class: 'form-control subgroup-filter')
 
   %table.table.table-bordered
     - @participants.each do |p|
             = render partial: "activities/presence_buttons", locals: {activity: @activity, person: p.person, state: p.attending}
 
 .hidden-sm.hidden-md.hidden-lg
+  .panel.panel-default
+    .panel-heading
+      = t 'activerecord.attrs.activities.subgroups'
+    .panel-body
+      = select_tag(:subgroup_filter, options_for_select(@subgroup_ids), class: 'form-control subgroup-filter')
+
   .panel.panel-default.panel-success
     .panel-heading
       %a{role: 'button', href: '#present-collapse', data: {toggle: 'collapse'}, 'aria-expanded': 'false'}
     %table.table.collapse#present-collapse
       %tbody
         - @participants.where(attending: true).each do |p|
-          %tr{data: {person_id: p.person.id, activity_id: @activity.id}}
+          %tr.participant-row{data: {person_id: p.person.id, activity_id: @activity.id, subgroup_id: p.subgroup_id}}
             %td
               = p.person.full_name
               - if p.is_organizer
               - if p.person.id == current_person.id || all_buttons
                 = render partial: "activities/presence_buttons", locals: {activity: @activity, person: p.person, state: p.attending}
 
-          %tr{data: {person_id: p.person_id, activity_id: @activity.id}}
+          %tr.participant-row{data: {person_id: p.person_id, activity_id: @activity.id, subgroup_id: p.subgroup_id}}
             %td{colspan: "2"}
               = editable p, :notes, url: presence_group_activity_path(@activity.group, @activity, person_id: p.person_id), title: t('activities.participant.notes'), value: p.notes, emptytext: "--"
 
     %table.table.collapse#unknown-collapse
       %tbody
         - @participants.where(attending: nil).each do |p|
-          %tr{data: {person_id: p.person.id, activity_id: @activity.id}}
+          %tr.participant-row{data: {person_id: p.person.id, activity_id: @activity.id, subgroup_id: p.subgroup_id}}
             %td
               = p.person.full_name
               - if p.is_organizer
               - if p.person.id == current_person.id || all_buttons
                 = render partial: "activities/presence_buttons", locals: {activity: @activity, person: p.person, state: p.attending}
 
-          %tr{data: {person_id: p.person_id, activity_id: @activity.id}}
+          %tr.participant-row{data: {person_id: p.person_id, activity_id: @activity.id, subgroup_id: p.subgroup_id}}
             %td{colspan: "2"}
               = editable p, :notes, url: presence_group_activity_path(@activity.group, @activity, person_id: p.person_id), title: t('activities.participant.notes'), value: p.notes, emptytext: "--"
 
     %table.table.collapse#absent-collapse
       %tbody
         - @participants.where(attending: false).each do |p|
-          %tr{data: {person_id: p.person.id, activity_id: @activity.id}}
+          %tr.participant-row{data: {person_id: p.person.id, activity_id: @activity.id, subgroup_id: p.subgroup_id}}
             %td
               = p.person.full_name
               - if p.is_organizer
               - if p.person.id == current_person.id || all_buttons
                 = render partial: "activities/presence_buttons", locals: {activity: @activity, person: p.person, state: p.attending}
 
-          %tr{data: {person_id: p.person_id, activity_id: @activity.id}}
+          %tr.participant-row{data: {person_id: p.person_id, activity_id: @activity.id, subgroup_id: p.subgroup_id}}
             %td{colspan: "2"}
               = editable p, :notes, url: presence_group_activity_path(@activity.group, @activity, person_id: p.person_id), title: t('activities.participant.notes'), value: p.notes, emptytext: "--"