Implement ezp 20321

_Note: this pull request depends on https://github.com/ezsystems/ezpublish-kernel/pull/170 by @pspanja._ Translation handling of files in this PR depends on the refactoring done by Petar, since it adds a `copyLegacyField` callback to the Storage Handler, which it depends upon..

*It isn't meant to be merged as is, but should be rebased once https://github.com/ezsystems/ezpublish-kernel/pull/170 has been merged into master.*

It implements cluster support for binary FieldTypes (Image, BinaryFile, Media) by means of a `LegacyFileService`.

Tasks:
- [x] Refactor the FileService
- [x] Create LegacyFileService
- [x] Adapt FieldType: BinaryBase
- [x] Adapt FieldType: Image
- [x] Adapt FieldType: BinaryFile
- [x] Adapt FieldType: Media
- [ ] Refactor MetaData handling