Allow use of multiple rqworkers

[p-rintz]

This closes issue #129
I oriented myself based on the netbox-rq.service of the main netbox project.
I removed the reload of the rqworker and used a restart instead, as the service file from netbox does not have a reload.

Default install stayed at 1 process.

• Allow use of multiple rqworkers
• Add tests for changed rqworker processes

[lae]

Content of the changes looks okay to me. I can't test it out atm, but perhaps @tyler-8 might want to take a look at this?