(#3087) - simpler putLocal/removeLocal for idb

I also got rid of the additional `_doc_id_rev` index, because it seems totally unnecessary. We have to do a `get` anyway, so that `get` might as well just be for the id instead of the id+rev.

Performance improvement as measured by the `temp-views` test:

firefox 35: 37989ms -> 36618ms (3.6% improvement)
chrome 39: 14915ms -> 13979ms (6.2% improvement)