Allows a job to be executed when no other jobs are allowed to run

The pre-job steps are:

1. The plugin will initiate a shutdown mode which means that no other jobs can be started.
2. It waits until every job except this one has finished, unless it is indicated not to wait through optional flag. 
3. Then it starts to execute the job.

The post-job steps are:
1. Inactivates jenkins shutdown mode

Combining this plugin with for instance scheduled build will pause the build queue. When this job is done, it unpauses the build queue.

Plugin was created by Marco Ambu but almost completely rewritten by Sam Tavakoli. 
Fernando Miguélez added lenient mode, which skips waiting on running jobs, and Spanish translation.