Bring in categories from using repo

[mcwhittemore]

Currently this dictates the categories you have. It would be better if this was something provided as a config from the using repo.

[jimthedev]

Hey, Commitizen author here. Just saw this issue. I'm trying to brainstorm a bit on a protocol or config for repo adapters to be able to access the config.commitizen object from the using repo's package.json.

It is being tracked here. I'd welcome any suggestions on how we can improve core to support this kind of thing.