Almost decouple layouting and drawing in vty frontend.

Also fix jumping modeline.
Extract some layout code from Yi.UI.Vty into Yi.UI.SimpleLayout.
Try --force-reinstalls in attempt to fix travis build.
Remove some unneeded code.
Label main vty thread.
Move some more layouting code to Yi.UI.SimpleLayout.
Yi.UI.Vty now completely delegates layouting windows to Yi.UI.SimpleLayout

Still todo: extract layouting of tabbar items.
Merge remote-tracking branch 'origin/master' into vty-refactoring

Conflicts:
	yi/src/library/Yi/UI/Utils.hs
	yi/src/library/Yi/UI/Vty.hs
Tweak vim autoindent after n_o and i_<CR>.
Allow frontends to submit multiple events at once.
Fix some warnings.
Now I'm just using travis to compile pango frontend.
Update vty dependency.
One less boolean in API.
Trying to blindly fix pango again.
Further get rid of YiString <-> Text casts

This removes most of the TODOs which required changes on yi-rope side.
Looking at the profiling output, all the resources are going into
rendering or rendering-related shenanighans (getStream') rather than on
spurious conversions elsewhere.
Minor style/comments
Kill a few unused functions
Huge pango performance boost in common case

See the diff for details. It boils down to asking pango to render much
less text.
Update CHANGELOG