Added two checkbox parameters, autoCloseFailed and autoMergeStable

...ing each project to determine this automatic behavior if wanted.

This implements a request for auto merging #65, and my own personal request similar, to auto close but gives the option to the project configuration.

https://github.com/timols/jenkins-gitlab-merge-request-builder-plugin/issues/65
Do we not risk throwing a `NullPointerException` here? Users who have upgraded from an older version of this plugin will return a null value for `getAutoCloseFailed()` which Java will attempt to auto-box as part of the comparison here.