Allow ability to hide certain hashtags

Create a "Hide hashtag" setting where users can toggle certain hashtags to never be seen again (in boost or in discovery) while browsing the site. Any time the selected word shows up in a piece of content (hashed or not), it will be blocked from view for the user.

Add list to settings showing all hidden hashtags, next to blocked channels. From here, user can remove any hashtags they have hidden.

If a channel is opted into a hashtag, but opted out of another one and a piece of content contains both, the opt-out will override and the user will not see it.