Modify method store_file of interface Store, to return the modifie date of the uploaded file in the store
Add method get_updatetime to class WriteWorker, to get the time when the file has been uploaded to the store
Bugfix class WriteWorker, to accept float value as returned modify date (important  if no value is returned, as the end time is then used instead, which is a float)
Modify class StoreSyncThread to update the modified date of a file after an upload
Bugfix cache, which would refresh a cached entry from the store, even though it is up to date because the local modified date is older than the modified date in the store
Bugfix StoreSyncThread, consider that setting a cache entry to be non-dirty will delete the entry if the cache size is exceeded
Bugfix class RemoveWorker, actually delete files in the store
Bugfix method delete of class StoreSyncThread, do not restart RemoveWorkers, since they could later remove a different file with the same path  that has been written after the inteded deletion of the file
Bugfix class GetFreeSpaceWorker, a thread needs to be recreated, before it can be started again
Update setup.py with new version
Modify README.rst, add instructions on how to automatically login to dropbox
Update CHANGELOG with new version