refactor: move layer list into partial that can be included in app template
refactor: clean up ITiledMap implementation

- Remove IEditableTileLayer and make ITileLayer contain relevant editable info
- add PowTileMap implementation to be used by various formats to insert and extract data about tile maps
- Fix a few issues in layers list ui
chore: extra meta attributes on page
refactor(PowTileMap): clean up separation of concerns issues

 - move knowledge of view and rendering system outside of PowTileMap.
 - add event notification for modifications to tileMap, and have view respond to them.
 - remove layer selection and visibility actions as they're not _super_ useful.
 -
chore: fix up broken tests from refactoring