Chinese translation at 68% completion.

Added all the missing translation strings towards the end of the file.
Added license section

Added license section with link to license
Merge pull request #154 from benhc123/patch-4

Added license section
Updated android build tools version to 21.1.1
Removed duplicated entries from zh strings.xml.
Another try to shutdown.
Implemented finish of all activities.
Implementing destroy of EngineService.
Implemented music service shutdown.
Found a point to halt the process without restarting.
Un-registering engine receiver in shutdown.
Considering the shutdown situation in ImageLoader.
Added UI menu exit button.
Fixes issue #155

Just made `setOptionalIconsVisible` public, now the class can be found.
Weird.
Changelog update.