WIP: Support flowdock, team-based routing, small fixes

[nabadger]

Hey,

This is a bit of a huge PR so I understand if you don't want it :)

It might be of use to you still, so any comments welcome, or just take any bits you are interested in.

Essentially it:

• Adds a yaml configuration file to support multiple notification methods (I call them receivers)
• Adds 3 new annotations
  • kube-lookout/enabled: Only notify if True
  • kube-lookout/team: Maps to a 'team', which is essentially a channel/token combination
  • kube-lookout/receiver: Maps to a receiver (flowdock/slack)
• Deal with the case where no pods come up (should go into degradation state)
• Readme updates
• Update example manifests so that credentials are handled in a Secret resource type
• Default to a kube-lookout namespace (I'm not sure it's very common to populate kube-system by default)
• Move to pipenv and bump latest packages (because I couldn't get pinned packages to work)
• Move to deb-slim (just a personal preference here as we tend to run into issues with python/alpine in the past).

I still need to add tests for flowdock.

[nabadger]

Haha yeah no worries

[dmarkey]

The build doesnt pass :(

[nabadger]

I'll take a look at that :)

[antonblr]

The build doesnt pass :(

Perhaps need to update .travis.yml with:

install:
  - 'pip install pipenv'
  - 'pipenv install'

[nabadger]

I think these changes are too big for a PR at the moment.

I'll close this and think about creating a smaller set of PR's which should be easier to pull in if required.