[vim] Highlight insert mode

- Highlight the cursorline only in insert mode.
[vim] Added tab-bracket matching

Simple tweak to match bracket pairs with the <tab>-key.
[vim] Back to powerline

Back to powerline
The color highlighting between the different modes "just works"!
[vim] Clean plugin management

- Moved vundle-related management into it's own file
- Removed dmenu file searching
[vim] Fix kludges with startup

After intensive duckduckgo'ing, I seem to have found a somewhat dirty cure
for the weird startup behaviour I've been experiencing lately.