Refactored structure.
Merge pull request #17 from blaugueux/refactored-flow

Major refactor of flow and organisation

Move all Symfony related commands into a symfony.rake file
Move all deploy hook related stuff into a deploy.rake file
Add a new symfony:assetic:dump command with configurable flags
Add configurable flags to symfony:assets:install command
Improve the doc
Remove symfony:assets:install from the default hook structure. For projects using SensioDistributionBundle this task is already run during composer install.
Remove `composer_install_flags`