This initial PR just adds a enable_experimental_hashtag_autocomplete
setting, and related JS & HBR files, replacing direct setup of
the autocomplete within d-editor and instead using the new
lib/hashtag-autocomplete. This is the beginning of preparations
to allow other data sources to be added to this autocomplete,
as well as a redesign of the menu and rendered tags in the composer
preview and posts.
Martin Brennan
472abe532e