Update common.py for Bootstrap

Add new CSS file source and output to the django_pipeline settings
Add Bootstrap-sass
Create bootstrap.scss.mako
Update common.py

Correction.
New version of Font-Awesome
Boostrap - gem to direct SASS files
Font-Awesome correction
Font-Awesome correction
CSS Pipeline correction
Bootstrap customizations
Bootstrap correction (SASS error)
Bootstrap customization
Bootstrap modifications
Revert Font-Awesome
Remove unused file
Add Bootstrap-sass
Create bootstrap.scss.mako
Font-Awesome correction
Revert Font-Awesome
Remove unused file