exclude archived projects

[Raytion]

Following the example for the GitHub Plugin (linked in discussion) this PR adds the configuration option to exclude archived projects from the list of projects that are built by jenkins. Posthum archived projects are removed from the project list on the next scan.

fixes #118
https://issues.jenkins.io/browse/JENKINS-63610

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  -> There are no unit tests for GitLabSCMNavigator to begin with, to use as orientation. The fix was integration-tested on a local Jenkins instance.

[grazius]

this pull request can be integrated in the next release ?
it's gone to be a real problem with a lot of projects that close or open on a private gitlab