Fixed exception when loading images with 'images-versioned' path

> Fixes http://jira.ez.no/browse/EZP-22781
> Status: open for review

### Changes
Replaces the regular `IOService` in `FieldType\Image\ImageStorage` with a `FieldType\Image\IO\Legacy` one.

It implements the same interface (also created an interface for IOService), but dispatches calls between two IO services: the regular one, operating on 'var/storage/images', and one dedicated to draft images, operating on 'var/storage/images-versioned'. It does so by checking the path for some strings taken from the ConfigResolver.

As a side benefit, this simplifies ImageStorage, since more legacy specific details are moved out to a legacy specific service. The only thing that remains is the XML, if I'm not mistaken.

Note that it (+ the Container/tests changes) required changes the File based FieldType integration tests, but it overall simplifies things. The temporary folder should also be properly cleaned after tests.

### Open questions
- [x] I'm really not convinced with how ezimage services are declared... especially those that are only for legacy. Can we leave it that way for now, and clean it up later ?
- [x] Create a factory for `FieldType\Image\IO\Legacy` that takes care of settings (hash passed to ctor)
- [x] Try to move test files back to `/tmp`.
- [x] Unit test `FieldType\Image\IO\Legacy`