TweetListEntry: Remove the rt_label if the tweet is no rt
TweetListEntry: Slight refacroting
TweetListEntry: Remove the delete menu item if it's not suitable
TweetListEntry: Make the time delta just text

we will introduce the link in the tweet details.
TweetListEntry: Move the hover buttons to the right

So they just consistently keep their position no matter what. Will also
simplify pretty much everything.
UserStream: Also print the acccount name on heartbeat
TweetListEntry: Correctly set the hover_box's margin_right
TweetListEntry: Also adjust the hover_box on retweet

... that is, if the tweet is retweeted from another client/device and we
only get the event from the Twitter server, nothing else.
HomeTimeline: listen to (un)favorite events

and mark the appropriate entries as (un)favorited.
HomeTimeline: Correctly mark tweets as unretweeted
MentionsTimeline: Implement deletion, rts, favs

... with stream events.
MentionsTimeline: Fix unfavoriting

which I accidentally broke in the last commit.