Per-repository and per-module configuration

[timothyb89]

The bot tries to auto-detect as much as possible, but this isn't always feasible. It should be possible to store per-repository and per-module configuration in git to specify various options:

• versioning policies
• dependencies to ignore
• notification settings or templates
• possibly extra user-defined plugins that should be run on repository events (e.g. run some js when a new issue is filed)

[timothyb89]

More thoughts:

• user defined templates for notifications, etc now that we have nunjucks
• hooks for events (including github events) possibly using something like vm2