Smoke test template finished

[theinze]

Smoke test template now operational: Idea, execute the demo_*.py scripts and see what happens

• [x] Flavor 1: Compare the figures generated by the scripts (see tests/smoke_test.py and tests/base_images/)
• [x] Flavor 2: Just look if there are no runtime errors/exceptions (see tests/smoke_test.py)
• [x] I am now using the nose testing framework, but that does not mean any changes to you

In order to become operational, it would be nice if the demo_*.py scripts are working again, currently, only the demo_doublet.py script is working, which is also used for the image comparison ...

[joha2]

Nice pull request! Some little remark: Also demo_mirrors.py and demo_optimize.py are working again :-)