Issue #2330899 by attiks, Jelle_S, fietserwin: Allow image effects to change the MIME type + extension, add a convert image effect.

Issue #2272481 by herom, ParisLiakos, tim.plunkett: Remove usages of watchdog() from forms, plugins and controllers.

Issue #697760 by sun: Replace getInfo() in tests with native phpDoc + annotations (following PHPUnit).

Issue #2211227 by mondrake, xjm | fietserwin: Refactor image and imagetoolkit: isExisting, isSupported, supportedTypes, getMimeType.

Issue #2217783 by mondrake: Remove $extension and $mimeType from Image, use image_type_to_xxx function in the getters instead.

Revert "Issue #1356602 by nicholasruunu, mcjim, rteijeiro, chrisjlee | jenlampton: Clean up icons in misc."

This clean-up accidentally introduced a few regressions, so rolling back until it's ready.

This reverts commit fab42693.

Issue #2103621 by mondrake | fietserwin: Move GD logic from ImageInterface to toolkit, tie toolkit instance to Image instance, toolkits should no longer be instantiated separately.

Issue #2048827 by claudiu.cristea, tim.plunkett: Move Image toolkit API from system.module to Drupal\Core.