JSON.parse only folder descriptions (not documents) in the wireclient (rebase1)

rebase of #693

While thinking about the [bug we discovered with webmarks](https://github.com/remotestorage/remotestorage.js/pull/693#issuecomment-45077759) that the subtrees of nodes that have a 'remote' version, should be treated as outdated, and fixed that in 32b5e2f

While checking out the branch to fix it, I realized it was still using a broken version of `isOutdated` so I also had to rebase it first.