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
Change the parameter types to `boolean` so they have automatic false values if not specified then remove these `if` blocks.