[WIP] Add image tests

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

Currently this contains only an image test page and a web test case. It tests the image form type, integration with imagine and displaying images.

**TODO**
* [ ] add unit tests
* [ ] maybe remove some tests from the web test and validate it by the unit tests as it becomes slow?