change PCL condition upload to work with new Dropbox

The new Dropbox has a REST interface, so instead of uploading
the condition payload and metadata files to a directory on
the dropbox host, we make a call to the REST API.

Requires putting the cmsprod username and password into the
Tier0 configuration. I don't like it, but it's the only way
to make that work for now...
Merge pull request #4029 from hufnagel/newdropboxupload

change PCL condition upload to work with new Dropbox