Test invalid observable

Branch coverage told me I didn't test an if-statement fall-through.  Nice.
Add intermediate conversions for equatorial

Add intermediate steps.
Distinguish between HiSPARC azimuth and horizontal Azimuth.
Add more information about input for date to JD.
Add unit information for ECEF to ENU.
Improved alignment of transformation matrix.
Merge pull request #42 from HiSPARC/refactor_simulations

Improve simulation test for invalid observable
Fix bug in ErrorlessSimulation
Fix typo reported in #41

Also get event_header and event_end from correct location.
Those attributes have been moved to the root in the corsika.h5.
Old corsika.h5 still had the attributes on the groundparticles table.
Update groundparticle test data and result

Use same corsika.h5 as used by the corsika test.
Change simulation input arguments to get more hits.
Add some tests for detector simulation
Update docstrings in corsika module
Use transformation.axes for coordinates in cluster
Add tests for groundparticle simulations

Test for getting particles in groundparticle simulations
Test for the query string used to get particles
Remove unused imports in test simulation detectors
Additional comment about coordinate transformation
Remove some unused code

Remove code that prints nice formatted text when
printing CORSIKA data from a DAT00000 file.
Further tests for groundparticle simulations
Add test for API

I see that if allow_stale is True the wrong result is returned!
Bump version to 0.9.21

Fixes:
- CORSIKA coordinate transformation
- celestial transformations
- particle query for groundparticle simulations
- bug in errorless simulations
- more tests for some parts
Enable transformation tests

Forgot to add init for transformation tests
Improve data download

Use get or create for events and weather table.
Allows multiple calls to download_data to same group.
Bump version to 0.9.22

Enable transformation tests
Improve esd.download_data to allow multiple calls
Improve test for detectors
Merge branch 'master' into tom_corsika