Add bundle to .gitignore

Bundles are now handled via Vundle so there's no need to monitor
the bundle directory as everything is done through the :Bundle
command
Change vimrc to use Vundle instead of pathogen
Move mapleader definition to vimrc

It seems that the mapleader has to be defined before vundle starts
to load the plugins. For this reason, I moved it from yadr-keymap
back into the vimrc. I'm sure it's not a big deal having the leader
mapped under the "general config" instead of inside settings.
Remove csapprox

Since we're now able to install Solarized on iTerm2, there's no
need for approximating the theme when using vim instead of
mvim. In fact, using csapprox on iTerm2 with solarized installed
breaks the theme completely.
Update Rakefile to manage pathogen-to-vundle upgrade

The Rakefile now detects if pathogen is installed and in that case
it performs the following operations:
1. Moves vim/bundle to vim/bundle.old
2. Removes all the submodules from git config and cache
3. Initializes and updates the new submodules (zsh and bundle)
4. Runs the vundle installer that takes care of the rest