require sonata admin bundle

- necessary for tests
- we must specify what the target versions are
ignore composer.lock and vendors

It is a library, there is no point in versioning the composer.lock
require phpunit in the development environment
remove reference to missing file
test the finder provider
test finder provider service creation
improve and test compiler pass

The compilation no longer fails with an empty container.
Copy and adapt from doctrine orm bundle

This commit should be fixed up later.
create proxy query
create pager
create datagrid builder