Run :AirlineRefresh when opening netrw.

The goal of this was to fix an annoying bug in which running `vim .`
(opening vim to a directory) gives a whole stream of errors. The
solution is to press :<Enter>. I thought that this might help, but no
cigar.
Disable matching bracket highlighting.

This makes scrolling through Objective-C code painfully slow (i.e. a
second or more every time you go over a bracket).