Add option to remove offline support

[TheModMaker]

Offline support requires including sqlite (which is provided by iOS) and protobuf. These can be large dependencies that may not be needed. We could add an option to remove offline support to reduce the size of the binary. Most of offline is separate in a few classes, but there is the ValueType enum which is used around the library. The best option would be to store a raw number in the proto and keep the enum in C++; we'll then just need to cast it when we read/write to the database. This is a reverse-compatible change.