style: display loading animation during page load

- bring over animations and transition styles from pow2 (consider moving to pow-core).
- hide all the ng- directives on screen until app is initialized.
- display "loading..." mesage before app init.
feat(TileEditorTool): support custom cursors for tools

- add setCursorClass(name:string) to TileEditorTool which takes a CSS classname to apply to the editor view, that should contain the needed styles to change the cursor.
- any specific tool cursor is removed when the tool is deactivated.
- update HandTool to support hand cursor where available.
feat(TileEditorTool): add zoom tool