v2.0 features

This PR introduces new features:
* filters, sorting and scopes via related fields like `tags.name` or even `shop.owner.adress.city.name`
* rename the package on packagist to `symfony2admingenerator/generator-bundle`
* dynamic filters form allows you to build complex filtering conditions
* use the same form type for New / Edit and Filters form

This PR also introduces some changes:
* the assetic layout `base_admin.html.twig` now bundles the assets into packages (`admingenerator_js` and `admingenerator_css`)
* the assetic filters have been changed to `uglifycss` and `uglifyjs2`

This PR is still not complete, there are some TODOs:
* **most important** rewrite documentation!!
* fix/write new tests to match new features

This PR has only been tested for Doctrine ORM! This needs testing for DoctrineODM and Propel.