Fix EZP-22280: Implement a native image AliasGenerator

> https://jira.ez.no/browse/EZP-22280

This PR implements a native image alias generator, using [Imagine lib](http://imagine.readthedocs.org/en/latest/) with the help of [LiipImagineBundle](https://github.com/liip/LiipImagineBundle/).
However, while interfaces provided by LiipImagineBundle are implemented and services properly exposed, `AliasGenerator` directly uses eZ specific DataLoader and CacheResolver.

Depends on:
* https://github.com/ezsystems/ezpublish-community/issues/187
* https://github.com/ezsystems/ezpublish-legacy/issues/1079

## TODO
* [x] Implement LiipImagineBundle interfaces
* [x] Fix [blocking issue EZP-23349](https://jira.ez.no/browse/EZP-23349)
* [x] Implement siteaccess aware configuration for filters
* [x] Port existing geometry filters (e.g. `geometry/scaledownonly`)
* [x] Implement mechanism to remove image aliases when trashing/deleting content (`SignalSlot` for content repository integration, `ezpEvent` for legacy admin integration)
* [x] Tests
* [ ] Deprecate old image settings (e.g. imagemagick)
* [ ] Doc
So it can be reused/tested. But as long as it is needed only here, you are right.