Coord trafo

[tino-michael]

added a module that contains some low-level coordinate transformation functions to bring various coordinate systems into the convention that is expected by my reconstruction tools -- i.e. right-handed x-y-z coordinate system with z->upwards and phi and theta in the standard (?) definitions: theta, angle to z-axis and phi, angle in the x-y-plane from the x-axis towards the y-axis.

By this approach, assuming that azimuth is measured from north towards east, the x-axis points north and y points west, so phi = -azimuth.
The camera coordinates are mirrored along the x-axis, so that y points "up" and x to the "right", as it is expected by pixel_position_to_direction.

[codecov]

Codecov Report

Merging #580 into master will increase coverage by 0.02%.
The diff coverage is 90.9%.

@@            Coverage Diff             @@
##           master     #580      +/-   ##
==========================================
+ Coverage   63.22%   63.24%   +0.02%     
==========================================
  Files         174      175       +1     
  Lines        9523     9537      +14     
==========================================
+ Hits         6021     6032      +11     
- Misses       3502     3505       +3

Impacted Files	Coverage Δ
ctapipe/utils/__init__.py	100% <100%> (ø)	⬆️
ctapipe/reco/HillasReconstructor.py	95.79% <100%> (-0.33%)	⬇️
ctapipe/coordinates/__init__.py	100% <100%> (ø)	⬆️
ctapipe/utils/linalg.py	87.87% <100%> (ø)	⬆️
ctapipe/coordinates/coordinate_transformations.py	86.95% <86.95%> (ø)

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[kosack]

could you move the /utils/coordinate_transformations.py file to /coordinates/? It makes more sense there