Don't use cache before the initial sync is finished

fix sync setting cache ready (with test)

fix https://github.com/remotestorage/remotestorage.js/pull/509#discussion_r8013775

refactor https://github.com/remotestorage/remotestorage.js/pull/509#discussion_r8013810

self-explaining code https://github.com/remotestorage/remotestorage.js/pull/509#discussion_r8013807

remove put/delete that is irrelevant for this test https://github.com/remotestorage/remotestorage.js/pull/509#discussion_r8013816
don't go to remote if not connected

fix missing ')'
make caching#cachePathReady dependent on local#onCheckLocal
typo checkLocal -> _checkLocal