Cleanup cached preview images on uninstall

Change-Id: I9267a160fbabeb67ade2f18fdaf8d8c6acc539da
When applied theme is removed, revert to default

Fixes issue where fonts and other resources do not get reverted
properly when an applied theme is uninstalled.

Change-Id: I30c9ea018f8bffc6aff51c5b38ff1e4ec82b7b20