appview: db: follow: add GetFollowers and GetFollowing functions to fetch Follows #483

this is pretty cool! couple of points:

• the GetFollow* methods are a bit repetitive (in part due to the database/sql APIs), can we dedup them like we do in the rest of the codebase? the approach we use here is to write GetItem(e Execer, filters ...filter) ([]Item, error) and then use filters to create more specific getters. you can look at db/spindles for an example
• we could do something similar for GetFollowStatus i think

made a GetFollows, and made the GetFollowers and GetFollowing use that (and also removed GetAllFollows since its not necessary with GetFollows)

oops T.T actually fixed it