Jenkins integration

[beauof]

• [x] set up Jenkins build server
• [x] weekly testing of cbm-software/iron repo (devel branch) using keytests target
• [x] allow users to trigger tests on demand
• [x] modify python script with matplotlib to also work without X server
• [ ] modify cmgui scripts to work without X server
• [ ] use cbm-software/iron-tests for pull-requests and nightly tests of cbm-software/iron
• [ ] automated tests of pull-requests
• [ ] automated merge of successful test of pull-request

[maierbn]

• [x] modify python script with matplotlib to also work without X server

edit by @beauof: Included item in list above.