Added in previous commit from pull request #4663
As discussed, we do not need this option so no need to introduce
a new dependency on the config file in the sync engine
* Add checksums/supportedTypes and checksums/preferredUploadType
capabilities. The default is that no checksum types are supported.
* Remove the transmissionChecksum config option. Servers must now
use the capabilities to indicate that they are fine with the
client sending checksums.
Note: This intentionally breaks brandings that overrode
Theme::transmissionChecksum. The override must be removed and the
server's capabilities must be adjusted to include the new values.
