Template based job creation

Adds capability of creating new projects for repositories with no job, using an existing Jenkins job as template, either using a single template for all unknown repositories or based on the repository name or group.

Although it doesn't merge automatically, I've cherry-picked the commits producing the conflicts and solved remaining ones, so it is safe to merge manually accepting changes from my branch (using -Xtheirs).

The only test I've not been able to fix is

    spec/values/project_spec.rb:113 # GitlabWebHook::Project when determining if matches repository url and branch when parametrized does not match when branch parameter is not of supported type

which produces a "only string parameters for branch parameter are supported" warning instead of the expected exception.
Yes, it seems to me that we should separate matching job finding and automatic creation from actual build. The way I see it, if automatic creation is enabled:
* find an exactly matching job
* if it doesn't exist, find a matching template
* create a new job matching the new payload exactly
* trigger that job
I've made some comments on the other PR for readme, so maybe we can discuss there.