Merge pull request #15 from Longor1996/master

(Big) Lot of small changes.
fixed focus bug and updated build
added shift operation
updated build
optimised some image operations

some operations can be done with minimal or no data. eg: Invert

they use more memory in short term, which is garbage collected, and less in the long term.
new drawing system, image layering... big update
updated build
reimplemented editing functions
changed same-layer blending to replace
Blending using composites
added screenshot
update README
fixed image loading bug
Merged Update from HeroesGraveDev!

Other changes:
- Added simple custom Tree-Cell-Renderer for Image-Layer-Tree.