Scratchpad Python API

This is adding some Python API calls to the scratchpad and extending the scratchpad functionality a bit.

This has been brought up in a few places, most recently on Krita artists

• https://krita-artists.org/t/scratchpad-docker/3132/14
• https://forum.kde.org/viewtopic.php?f=288&t=133217&sid=3f97601c69c7fcbcaf15a28bb5ab7920

It does a few things

1. Ability to manually change mode from paint, pan, and color pick (this could be done before with mouse clicks only)
2. Ability to load and save images into it
3. Ability to select what you want to clear the canvas with
4. Added a new color picker icon. The existing ones didn't have the crosshair in the right position, so it didn't accurately show where it was color picking from.

This is a small animated gif of it using Scripter dialog

To Test: Grab the branch and build. You might have to do a clean build to update the python bindings. Open Scripter and paste in this text and run it.

scratchpad-demo-v3.py

The end goal is I want to turn this into a docker instead of the scripter dialog.