[vim] Disable Powerline fonts; set blank separators

It's too much hassle to ensure I have a patched font installed just to
make the airline plugin look pretty.
[profile] Give $GOPATH/bin lower precendence in $PATH

For security, it's not a good idea for Golang binaries installed using
`go get` to take precedence over system binaries. Adjust my `$PATH` to
prevent that.
[vim] Prevent Tagbar from opening automatically

Tagbar can be distracting - I'd rather open it when I need it.