Simplify and Groovyfy attachment handling

[mguillem]

Finally the complete pull request to handle attachments "in a Groovy way".

The original idea was here: #392 but it was still requiring an import that had to be whitelisted. This is not the case anymore and this change is particularly interesting as it removes the need for whitelisting JSONArray and JSONObject when using attachments.

[timja]

Thanks, I did try get this to work awhile ago but had issues passing an object in.
Nice work, code looks good, I'll merge if manual testing doesn't show any issues

[timja]

Functionality is great, thanks for doing this!
Can you revert the import ordering changes please
SlackSendStepTest and SlackSendStep

[mguillem]

import order changed (without explicit rules for the expected order it is just a requirement to demotivate contributors :-()

[timja]

Without explicit rules the default is always minimal change, which may mean deactivating auto import in the project you are in.

I will look at enforcing it with checkstyle soon

[jetersen]

@timja codacy has support for reading checkstyle rules but you can also setup Jenkinsci to do it, but Jenkins CI is a bit slower.

Code climate is another option

[jetersen]

on JCasC I would properly switch to code climate instead of codacy, https://docs.codeclimate.com/docs/checkstyle better documentation and better config

[timja]

@Casz checkstyle is already run as part of the build, there's just minimal rules.
I have a local branch but never finished cleaning up the codebase for it.