Bug 15794: Add an emoji picker to tag entry in OPAC

Bug 15794: Add an emoji picker to tag entry in OPAC

This patch introduces an emoji picker int othe OPAC's tag entry form.
It relies on the emoji-picker library [1]

To test:
- Apply the patches
- Restart all services (just in case some caching is taking place):
  $ restart_all
- Log into the OPAC
- Do a search, pick a record
- On the detail page for the record, click on 'Add tags'
=> SUCCESS: An input form is displayed, with an emoji picker on the
    right.
=> SUCCESS: Choosing an emoji populates the input with it
- Set 'TagsModeration' and retry
=> SUCCESS: Proposed tags are displayed correctly on the staff interface
    for tag moderation
- Sign off :-D

Sponsored-by: Hotchkiss School
[1] https://github.com/OneSignal/emoji-picker

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>