Modernize rotate to ZNE

[megies]

• don't do rotation from original input data to ZNE during startup anymore(which comes before optional instrument), but rather do it on the fly whenswitching between streams and do it after optional instrument correction, sothat instrument correction works properly and doesn't have to rely on metadata attached to traces which might not be valid anymore if all three channels do not share the same response
• get rid of some custom rotation code (that made it's way into obspy years ago) and rather just use the obspy high level rotate command and the complete Inventory for all data