Remove provident authentication

The implementation assumed basic auth without checking the mechanisms
supported by the server. Authentication should be handled by the http
client library, not the carddav plugin.
Fix photo downloading and cropping
Switch to Guzzle HTTP client library

With curl, it allows the reuse of the HTTP connection, which is why
addressbook sync is much faster with this library. We may get even
faster when using parallel connections for the multi-get processing.
cleanup
remove includes of deleted files
Guzzle: use RFC compliant redirect behavior

Fixes google contacts discovery
readd the crop_photo hook