Include an emoji picker

Summary:
Shows all emoji in categories, it will save the new emoji into the
clipboard.

Test Plan:
Manual testing; run `ibus-ui-emojier-plasma`
{F7573133}

Reviewers: #plasma, #vdg, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: hein, #vdg, GB_2, mart, ngraham, davidedmundson, broulik, plasma-devel

Tags: #plasma, #vdg

Differential Revision: https://phabricator.kde.org/D24454