Added 2.3 upgrade notes containing app_dev.php changes regarding debug component.
udpated the CHANGELOG for 2.3
Use kernel.http_method_override parameter
Install and configure bootstrap

bootstrap deps:
- jquery
- lessphp
Small typo/grammar fix.
Refactor assets management
Add assetic dumped files to .gitignore
Add some utility macros
Use bootstrap scafolding
Define a static navbar