EZP-21319: allow mulitple titles on the same level
EZP-21319: add level attribute on title element
EZP-21319: transformations for heading levels
EZP-21319: updated tests for titles with explicit level
EZP-21319: added additional tests for lossy conversion
EZP-21319: updated docs on ezxml lossy conversion fixtures
EZP-21319: tests: add seventh level heading
EZP-22279: Added dependency on DoctrineBundle
EZP-22279: Refactored storage engine factories to use Doctrine connections

Added notion of "repository" in the configuration.
Repositories are declared globally and used/specified at the SiteAccess level (or group).

A repository consists of an "engine" (to specify which storage engine to use), and config options for that engine.
In the case of "legacy", aka LegacyStorageEngine, a Doctrine "connection" is specified, which is configured in DoctrineBundle.
EZP-22279: Fixed tests
EZP-22279: Changed doctrine connection type hint from Doctrine\DBAL\Connection to Doctrine\DBAL\Driver\Connection (interface)
EZP-22279: Fixed LegacyDbHandlerFactoryTest
EZP-22279: Added tests for LegacyDbHandlerFactory
EZP-22279: Added tests for StorageEngineFactory
EZP-22279: Removed obsolete parameter ezpublish.spi.persistence.default_id
EZP-22279: Refactored StorageEngineFactory & LegacyDbHandlerFactory

Factors repository config retrieval + updated tests
EZP-22279: Added new "repository" semantic configuration
Added getConnection() to DatabaseHandler interface
EZP-22279: Added configuration suggestion mechanism

This mechanism eases semantic configuration migration.
It allows to display a nice readable message and a configuration snippet.
EZP-22279: Implemented configuration suggestion for deprecated database params.