Create DoctrineTestCase

The class can be used for conducting functional tests.
Add functional DQL paging tests
Merge DQL & ORM Query Builder pagers
Use Doctrine Paginator in DQLProvider
Create separate DoctrineORMPager

Previously the Doctrine ORM Query & Query Builder pager was constructed by
passing the necessary class names to a generic pager. It felt like having to do
too much work.
Rename DoctrineORMPager to ORMPager
Create separate Doctrine DBAL Query Builder pager

GenericPager was used previously to support Doctrine DBAL's query builders.
Fix namespace typo
Rename DQLPagingTest to ORMPagingTest
Create separate suits for unit & functional tests