Add support for geolocation and angles to msi reader

[mraspaud]

• Tests added
• Tests passed
• Passes git diff origin/master **/*py | flake8 --diff
• Fully documented

[coveralls]

Coverage decreased (-0.4%) to 65.508% when pulling f3c5d01 on feature-sentinel-2-msi-reader into 89217cb on master.

[codecov]

Codecov Report

Merging #305 into master will decrease coverage by 0.66%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master    #305      +/-   ##
=========================================
- Coverage   65.86%   65.2%   -0.67%     
=========================================
  Files         118     118              
  Lines       14336   14811     +475     
=========================================
+ Hits         9443    9657     +214     
- Misses       4893    5154     +261

Impacted Files	Coverage Δ
satpy/composites/__init__.py	32.93% <0%> (ø)	⬆️
satpy/readers/safe_msi.py	2.54% <0%> (-5.15%)	⬇️
satpy/readers/hrit_goes.py	41.59% <0%> (-9.09%)	⬇️
satpy/readers/safe_sar_c.py	19.32% <0%> (-0.68%)	⬇️
satpy/tests/test_scene.py	99.26% <0%> (ø)	⬆️
satpy/tests/reader_tests/__init__.py	96.55% <0%> (+0.12%)	⬆️
satpy/scene.py	83.33% <0%> (+0.3%)	⬆️
satpy/readers/file_handlers.py	88.88% <0%> (+0.65%)	⬆️
satpy/readers/yaml_reader.py	87.33% <0%> (+2.29%)	⬆️
satpy/readers/hrit_msg.py	29.81% <0%> (+4.58%)	⬆️
... and 1 more

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