Update deps and use @node-oauth/oauth2-server

[jankapunkt]

• use @node-oauth/oauth2-server
• update all dependencies to latest
• add code coverage to tests
• add GitHub actions CI
• replace jshint with eslint

Test this with your local setup by cloning this repo and checkout the branch 3.0.0

Other notes:

• we don't move to ES6 in this PR, because that would make the PR way too big!
• there are no functional changes in the code so it should be non-breaking (although the transition to @node-oauth/oauth2-server would be breaking if you used oauthjs before)

[shrihari-prakash]

Might also be a good idea to remove bluebird dependency since promises are native in a good amount of node versions. But I don't know if there is already a plan for this.

[HappyZombies]

Might also be a good idea to remove bluebird dependency since promises are native in a good amount of node versions. But I don't know if there is already a plan for this.

@shrihari-prakash I agree but let's keep that for another version/MR, this whole module should/will probably be refactored entirely at some point. The focus on this MR is to just update the node-oauth dependency and other deps.

[jankapunkt]

Thanks @HappyZombies @shrihari-prakash I will merge and then create a release under our org