The 'prepopulated-autocomplete-hashtag' plugin takes care of annotating #hashtags
with immutable entities and styling them a bit when the editor loads, in order to
decorate hashtags that could be present in the prepopulated text and to make them
behave exactly like hashtag entities that are generated by draft-js-mention-plugin.

Hashtags written by users after the editor loads are handled by draft-js-mention-plugin.

Two strategies coexist: prepopulatedHashtagStrategy is used to locate hashtags to be
annotated with entities in the text, and prepopulatedHashtagEntityStrategy is used
to locate hashtag entities in order to style them.
