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
This should be `boolean` rather than `Boolean` since we never expect it to be null.