GitLab

Tag incidents with organization names rather than UUIDs

See merge request !1

Because incidents are for human consumption.

Use a TTLCache with a 24 hour timeout.

When a secret is configured, expect all requests to contain a
X-Mist-Signature-v2 header with a signature: HMAC-SHA256(secret, body) -
otherwise, reject the request as unauthenticated.

Helps us detect WHERE incorrect secrets are configured in Mist

This still lacks a few significant features:
- Customer ID mapping to name
- Does not protect against duplicates
- Lookup of incident-to-resolve may not be robust enough

Also include pyargus into requirements, so we can talk to an Argus API
server.

Also, document the settings.

Because:
- This is more suitable when running in a container, as planned.

Additionally, reformat the code.