core: Verify MD5 sums after each transfer
drive: factor common authentication code into googleauth module

In preparation for Google Cloud Storage support
google cloud storage: Initial support for full Fs interface
google cloud storage: Make operations on single files work
google cloud storage: set the Content-Type from the file name
google cloud storage: implement ACLs and delete
google cloud storage: fix download of files in sub directories
dropbox: graphics for the Dropbox app (used in auth process)
dropbox: Initial support of full Fs interface

Still missing metadata support (eg SetModTime)
dropbox: basics of metadata in Dropbox datastore working
dropbox: Fix concurrent access to Dropbox datastore and Lower case keys in datastore
dropbox: Use /delta to list objects - much quicker

Also fix major performance problem - re-reading entry each time!
dropbox: open the datastore in the background
dropbox: Fix mkdir on already created directory
dropbox: remove metadata when we remove files
dropbox: make limited fs work (copy single file)
dropbox: Switch to using RFC3339 for time metadata
google cloud storage: Update metadata on Put since we get it back
google cloud storage: fix merge conflict

Conflicts:
	rclone.go
	rclonetest/rclonetest.go