Updated side panel UI

Updated side panel for Data, Actions, and Events to include +/- buttons and select lists. Obviously non-functional.
https://www.cs.drexel.edu/~sb679/Waved/ to view.

The only difference between what I did and the prototype is that for actions and events I included the word "Actions" and "Events" for consistency with the Data section. We can remove these later if we don't like them.

Covers https://github.com/KSHSK/WAVED/issues/26 and https://github.com/KSHSK/WAVED/issues/27 plus the data section which didn't have an issue.