Moved StoreUUID into a ubiquitous file.

[IMPROVED]  StoreUUID is now kept in a ubiquitous file and no longer in the key-value store.
            This allows us much better control over whether we have the current version of the StoreUUID
            and allows us to block until it is available before loading the store.  It further avoids
            bugs which might eg. cause new devices to create a new cloud store when unaware that one
            already exists and thus cause all other devices to lose their data.
Merge branch 'master' of github.com:lhunath/UbiquityStoreManager

Conflicts:
	UbiquityStoreManager/UbiquityStoreManager.m