Move Nav customizations into its own file

Considering the nav customization/cleanup code is fairly involved and
important, it shouldn't be hidden in the middle of cleanup.php
Allow the sidebar config functions to accepts args
Comment should be consistent
Return instead of echo class names
fix roots_fix_duplicate_subfolder_urls isset check

function checked if $matches[1] & $matches[2] were set, but next line operates on $matches[1][0] & $matches[2][0], so under certain circumstances, you get the following Notice: Undefined offset: 0.

Now it checks for the [0] offsets from the start.
Merge pull request #576 from jloosli/master

Fix bug on roots_fix_duplicate_subfolder_urls 
Unset menu bugfix. Support for additional classes.

Previous nav walker resulted in an error when no menu is set.
This fix supports supplementary classes i.e. nav-header nav-header-blue. 
N.B. Bootstrap classes (nav-header, divider, divider-vertical) must be added first. 
Add note about lib/init.php to README
Update docs for new sidebar exclusion method
Corrected spacing before pull.
Merge pull request #577 from Foxaii/master

Nav walker support for unset menu
Merge branch 'master' into grunt
Fix grunt watch Bootstrap LESS directory
Update French translation

Organisation - Typo - ...
Update to Bootstrap v2.2.0
Update to Bootstrap v2.2.0
Update conditional feed method
Update to Bootstrap 2.2.1
Fix for compatibility with ubermenu

Fix for issue #586
Merge master, update to Bootstrap 2.2.1