Image cache

Hi again.

Working hard on Grav... Next issue:

While in admin with image cache enabled, plugins like resize-images and other image manipulations targeted for the uncached versions are rerouted and execute their work on the cached versions. That's contra-productive as all manipulations are lost once the cache is cleared and even some are never used, e.g. in the filepicker field.

The culprit for this is located in ImageMedium.php, in its constructor. Definitely it would be great for plugin authors to be able to control cache / nocache by hooking into an event to bypass temporarily the cache for media manipulations.

Regards.
uh