Fixed EZP-23080: added inputUri property to Image\Value

> Status: work in progress
> Issue: http://jira.ez.no/browse/EZP-23080

Similar to #881, but for images.

`Image\Value` used the `id` property for both input and output. It made it hard to distinguish wether the provided value referred to a new image or to an already persisted one.

`path` is now mapped to `inputUri` when used for input.

This change introduces `inputUri`, dedicated to provided an input file. `id` can still be used, but an `E_USER_DEPRECATED` error will be thrown. This uses a newly introduced service `ezpublish.utils.deprecation_tester`. It has a `log()` method, and implements an interface suitable for mock based testing.

Non-existing property?