TODO

- code cleanup
    - switch to flask?
    - use a UI framework (react?)
    - cross browser support (touch?)

- drag element corners to resize

- on image upload, set appropriate dimensions

- store app metadata in database
    - allows exploring history/revisions and forks

- autogenerate boilerplace for action callbacks
- action callbacks dropdown (parse/run code without side-effects?)

- prevent assignment to actions, el?

- less obnoxious error messages

- run time error messages

- interactive console

- break points

- autocomplete

- more element types:
    - links
    - sliders
    - shapes?

- documentation / tutorials
    - especially for getting started

- drag-drop image uploads