Misc change to support loading dynamic summary/icon in app

- Add ThreadUtils.postOnBackground helper method
- Don't fallback to app.icon if tile's metadata contains icon uri
- Deprecate TITLE_RES_ID in favor of TITLE metadata

Bug: 63758074
Test: robotests
Change-Id: Ie60fb4677cdb12c3ff313ffdfdb4a4f4960fac0f