The repository code has been reworked a little to provide a better

interface for defining repository types, and to avoid hard-coding the

repository types everywhere.
Repository is now BaseRepository. It defines the type IDs for

configuration files that it supports, as well as the SCMTool name for

API queries. Common setup is performed in __init__(), reducing what

subclasses need to be responsible for.
This allows us to better abstract the repository support, which will in

time allow us to provide wider support for other SCMs.
Configuration is now less prone to failures. Missing configuration keys

now trigger a logging error, rather than crashing. Errors fetching

repository information are logged as well.
Unit tests have been added for configuration validation and loading, and

repository fetching.

Unit tests pass.