Filter by my reaction in search filter bar

• New filter in the search/filter bar, to filter by my reaction.
• Applicable to project issues list, project merge requests list, group issues list, project issue board list, project issue board modal, group issue board list.
• The list of frequently used emoji are based on all emoji that the current user has used, i.e. https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12962#note_36025227