Allow specifying extractors per telescope, fixes #1660

[maxnoe]

Use a TelescopeParameter for image_extractor_type and a dict[image_extractor_type] -> instanceof(ImageExtractor) for the actual extractors.

[codecov]

Codecov Report

Merging #1661 (9027ef8) into master (83d1a5d) will increase coverage by 0.00%.
The diff coverage is 92.68%.

@@           Coverage Diff           @@
##           master    #1661   +/-   ##
=======================================
  Coverage   90.43%   90.43%           
=======================================
  Files         186      186           
  Lines       13862    13887   +25     
=======================================
+ Hits        12536    12559   +23     
- Misses       1326     1328    +2     

Impacted Files	Coverage Δ
ctapipe/image/reducer.py	92.00% <70.00%> (-3.56%)	⬇️
ctapipe/calib/camera/calibrator.py	94.94% <100.00%> (+0.26%)	⬆️
ctapipe/calib/camera/tests/test_calibrator.py	100.00% <100.00%> (ø)
ctapipe/tools/display_integrator.py	96.37% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 83d1a5d...9027ef8. Read the comment docs.