Bugfix: Rely on `resharing` capability

The request to create a new share has been fixed so that it only includes the share permission
by default when the resharing capability is true, and the "can share" switch in the edition view
of private shares is now only shown when resharing is true.

https://github.com/owncloud/android/issues/4397
https://github.com/owncloud/android/pull/4472
