Improve Performance

[Glitchy-Tozier]

Is your feature request related to a problem? Please describe.
I used to use a Samsung phone, where images could easily be edited in the gallery app. It was fast and snappy.

I'm sad to say that ImageToolbox feels pretty slow in comparison. After many commands (for example cropping) there's a loading animation that makes you wait 1-2 seconds before allowing you to go onto the next step.

This slows down editing and also is an interruption of a user's worflow.

Describe the solution you'd like

First of all, try to fully optimize performance.

Secondly, if performance can not be improved, implement this idea to hide computations from the user:

1. When starting to edit an image, create a smaller thumbnail that's actually displayed to the user
2. All edits should be performed both on the visible thumbnail as well as on the full-resolution image behind the scenes
3. First perform operations on the thumbnail (much faster) and immediately display the result. This allows the user to keep editing. Only in the background work on the HD-image, without any indication to the user.
4. Only in modes where zooming in could be necessary (cropping, for example) should the real HD-image be displayed.

An implementation similar to this should eleminate most lagging and result in a much smoother user-experience.

Summary: Create a low-res preview that's displayed to the user instead of the original image. Perform all edits first on this preview. This results in much smoother editing.

[T8RIN]

I downscaled the thumbnail in some of the latest changes, it will be the part of the next release