Due to persisting bugs in tahoe's magic-folder status queue (which often displays inaccurate information or otherwise fails to reflect the number or state of queued upload/download operations), this PR (temporarily?) disables sync progress indicators from being displayed in the UI. Users needing to get a (very) rough sense of sync progress can still do so by watching the "size" status column (which increases as new files finish uploading), the newly-added "History" tab (which populates as files are added, updated, or removed), or the debug log (which now periodically prints the total progress and time remaining values as calculated from the magic-folder queue).

Proper status indicators will be re-implemented if/when the corresponding magic-folder bugs are fixed upstream (and/or when I figure out a sufficiently reliable workaround..). See #132