Use Vundle to manage Solarized vim plugin

Now that Vundle is installed, I can use it to manage Solarized.
Change Solarized diff mode to high

On 'high', it highlights changes in vimdiff by changing the background
color. On 'normal' (default) and 'low', only the text color changes.
Add git branch to status line

Fugitive provides a function to add the current git branch to the status
line. Setting statusline overrides the behavior of ruler.
Always display status line