feat: add githubapp auth

[Graborg]

motivation
This PR removes some minor inconsistencies/bugs but mainly it adds the option of authenticating as github app instead of a single user.
This makes it easier to manage use for organizations, without creating a dedicated user.

What kind of change does this PR introduce?
It add the option of running the service as a Github app. If the argument AUTH_AS_APP is omitted. The service will function as normal.

Did you add tests for your changes?
Yes.

Does this PR introduce a breaking change?
No

What needs to be documented once your changes are merged?
Nothing, already added.

[jnovack]

@yurm04 Has this project gone stale?

[yurm04]

@jnovack It hasn't! Thanks for pinging me.

@Graborg sorry for the HUGE delay and thank you for this PR. I'll take a look and will provide feedback 🙏

[yurm04]

@Graborg thanks for your patience. I'm trying to debug some failing tests in Travis CI before reviewing this PR. Sorry again for the delay 🙇‍♀

[yurm04]

@Graborg just starting to review and test this PR. When I try to run start or dev the app crashes:

> chronicler@1.0.0 dev /Users/****/Sites/Chronicler
> ./node_modules/nodemon/bin/nodemon.js --inspect ./src/index.js

[nodemon] 1.17.5
[nodemon] to restart at any time, enter `rs`
[nodemon] watching: *.*
[nodemon] starting `node --inspect ./src/index.js`
Debugger listening on ws://127.0.0.1:9229/773e274c-1e8f-45f6-9cd6-9cbe7a443479
For help, see: https://nodejs.org/en/docs/inspector
file:///Users/****/Sites/Chronicler/src/main.js:1
TypeError: fu.wrap is not a function
[nodemon] app crashed - waiting for file changes before starting...

I'm currently using:
node v10.17.0
npm 6.11.3
macOS 10.14.6

I tested master to make sure app runs there with current versions and seems to work. Could you post your system info and run this branch locally?

[Graborg]

Sure, I'll take a look. might have omitted something.

Thanks.