indexeddb backend

I replaced Local Storage with IndexedDB. I was able to test it in Firefox 33 and Chrome 38 without shims. I'm using IndexedDB objects there. The naming of the database is the filename and there is a store named "objects" inside each. Maybe the it would make more sense to use the directory as the database name and the filename as the store name, although it might add some complexity when managing DB versions since that requires to start a DB version change transaction, which requires you to close the opened databases temporarily.