chore: move services to top-level source directory

- It is used by editor/ and shell/ and potentially other editors in the future.
test: add behavioral tests for the $actions service
feat: add constant errors for throws in pow-edit
refactor: use constant errors in tile editor actions
chore: add errors.ts to grunt watch
tests: add behavioral tests for LayerSelectAction
refactor(TileEditorController): cleanup error strings and move some code in to directive
test: behavioral tests for editor actions

- remove TileEraseAction, which was just a paint action with 0 texture id.
- add comprehensive error detection to TilePaintAction.
- add pow2.editor.tests.TileEditorFixture that creates a tile editor and loads a test map.