CMIS Versions dialog: fix version date

The version creation date is more likely to be the
cmis:lastModifiedDate.

Change-Id: I15e81db6a4c5f638f3f472894608a8d6728dc2d2
CMIS Versions: removed a few useless buttons

Change-Id: I08a1593700495c2262a270cb9055e973ab0ede29
CMIS Versions dialog is experimental-only for the while

Change-Id: I39e2f3437045ae0ef7b33c65bb59f9fe201dcda7
OAuth2 application keys shouldn't be in the code.

The GDrive OAuth2 key is now defined at configure time. If either the
client secret or client id is missing, the Google Drive connectivity
will be disabled at runtime.

Tinderboxes can set up a GDrive key, but they need to make sure it's
not persisting in the build log.

Change-Id: I09bc748641ec14eae890f273f05bffe4ed421dbb