This PR fixes #300, ensuring that no magic-folders will be marked as "Up to date" in the UI unless their corresponding tahoe client is sufficiently connected to the storage grid (as determined by whether it has connected to enough nodes to satisfy the shares.happy threshold and has successfully completed a remote scan/crawl of the rootcap). The distinction between "Syncing" and "Scanning" has also been removed from the UI, since there was no functional difference between them from the user's perspective. Lastly, the total number of "connected" and "known" storage nodes -- along with the total amount of storage space available -- will now always be visible via the status label's tooltip (instead of via the now-removed "globe" button -- which served no other function).

Some additional -- and very minor -- code-quality improvements have also been included, in particular, constants (LOADING, SYNCING, UP_TO_DATE, etc.) are now used to more clearly represent folder-states instead of bare ints (0, 1, 2, etc.).