(#567) - fix websql adapter
(#567) - clean idb a little

It was done a little better in websql adapter so why don't we use
this in idb.
(#567) - fix in leveldb adapter
(#567) - fix isDeleted comment
Cleanup isDeleted in all adapters

We had that strange isDeleted(metadata, opts.rev) && !opts.rev
which results in isDeleted(metadata) because isDeleted is written
this way. And this results in isDeleted(metadata, winning revision)