[ENG-293] Tag assign mode

[jamiepine]

This feature makes assigning tags extremely simple and will be a prominent feature in the marketing material.

The tag button in the TopBar should hide the path view and instead show a line up of numbered tags, selecting some files and pressing that number will assign a tag to those files.

Another approach to this could be to have a floating tag picker UI that works in a similar fashion as above.

_{From SyncLinear.com | ENG-293}

[iLynxcat]

Accidentally auto-completed this when resolving some problems with GitHub. reopening as this is still WIP