Protobuf backup support

Server Changelog

• Added support for protobuf backups
• Removed support for legacy backups

Bug fix(es):

• N/A

Under the Hood:

• Library endpoint is removed and replaced by a "Default" category.

WebUI Changelog

• Added support for protobuf backups
• Removed support for legacy backups

Bug fix(es):

• N/A

Under the Hood:

• Better handling of empty genre strings