Add multiple assignee support to sidebar

app/assets/javascripts/gl_dropdown.js

app/assets/javascripts/issuable/issuable_bundle.js

...ipts/issuable/time_tracking/components/collapsed_state.js

...ipts/issuable/time_tracking/components/comparison_pane.js

...s/issuable/time_tracking/components/estimate_only_pane.js

...vascripts/issuable/time_tracking/components/help_state.js

...pts/issuable/time_tracking/components/no_tracking_pane.js

...ipts/issuable/time_tracking/components/spent_only_pane.js

...scripts/issuable/time_tracking/components/time_tracker.js

...avascripts/issuable/time_tracking/time_tracking_bundle.js

app/assets/javascripts/issue_status_select.js

app/assets/javascripts/labels_select.js

app/assets/javascripts/main.js

app/assets/javascripts/milestone_select.js

...avascripts/sidebar/components/assignees/assignee_title.js

...ets/javascripts/sidebar/components/assignees/assignees.js

...scripts/sidebar/components/assignees/sidebar_assignees.js

...ripts/sidebar/components/time_tracking/collapsed_state.js

...ripts/sidebar/components/time_tracking/comparison_pane.js

...ts/sidebar/components/time_tracking/estimate_only_pane.js