fixing JCasC compatibility

[ewelinawilkosz]

As reported in kuleuven#31 I broke the plugin.
After all the fix was a little bit more complicated and I used PR by @timja for slack plugin as an inspiration: jenkinsci/slack-plugin#404

it seems you can configure global configuration both manually and with jcasc now
you can also manually configure what's in the job

What's missing

1. Can't fill Notification message includes choice with proper options
2. Haven't tested if it actually works with mattermost - I'm not using it and if anyone here can spare some time on verifying with that version that would be great, if not I'll try to do that later
3. Haven't tested if it's working well with JobDSL (not sure if it could break but better safe than sorry)

So I'll continue my work to fix 1. But I wanted to share what I have so far, so anyone can contribute with some testing if you'd like

cc @jovandeginste

[jovandeginste]

@ewelinawilkosz Just tried your commit on our set-up, I can save the configuration

[ewelinawilkosz]

thanks for checking, but I'm hitting the wall - anyone has an idea why doFillCommitInfoChoiceItems is not filling "Notification message includes" dropdown list?

[ewelinawilkosz]

well... that's embarassing - f: was missing 😞

[jovandeginste]

@ewelinawilkosz deploying this change on our set-up, I will provide feedback

[jovandeginste]

@ewelinawilkosz seems to work, I will release this as a fix?