Improved drawing UI to make it easier to undo/redo and set and modify reference images.

This update also includes some minor bug fixes and improvements.

Thanks for all your great feedback and reviews :)

Support for undo and redo actions

• Updated app controls and made is easier to access color picker.
• Added reference image alpha slider and button to move reference image above or below art work.
• Minor bug fixes

Fix issues when purchasing Plus.

Minor Bug fixes

Initial release