v0.5.1 Alpha

- Preview mode runs sketches without installing them

- You must install the APDE Sketch Previewer once, but then you can run sketches without installation indefinitely

- Preview mode is available as another target, along with wallpapers, watch faces, and VR

- Support for the new Processing sound library

- Undo and redo are more accessible

- Ability to bypass screen overlay warning

- Lots of bug fixes

These changes are driven by GSoC '18.