Adapted color picker to support external selector movement

Used for editing categories.
Worked on edit category. See extended description

Still work in progress.

- Implemented auto movement of color picker to color of selected event
- Started implementation of checkers for constraining selection while
editing category
- Added cancel button and worked on UI
- Modularized population of category list to allow for proper update
upon addition, edition, or deletion.
- Tweaked validate method to allow editing events (WIP)