Fix Scene.available_composite_names showing unavailable composites

[djhoese]

This fixes an issue where Scene.available_composite_names would list composites that had missing dependencies. This has been happening for a long time apparently. So long that I don't even know how the previous code ever worked. @yufeizhu600 first pointed this out in #853 and if he could test this it would be much appreciated.

This PR mainly affects:

1. Scene.available_composite_ids/names
2. Scene.all_composite_ids/names

I've marked this as backwards-incompatible because I had to remove some functionality (kwargs) that didn't actually do anything useful and removed some functionality that I though would rarely be used. Mainly filtering what composites are shown by specifying what reader or sensors the compositors were based on or configured for. This is an unlikely use case so I made it so these keyword arguments can not be passed to the above mentioned methods.

The "available" methods now return the right composites from what I can tell. What might be surprising to some users is that all now returns less composites than it did before. That's because it is now checking that it actually knows about the dependencies required for a composite rather than just listing all configured composites. So if a generic Vis/IR composite asks for 11.0um band but the reader we are using will never have that band then that composite is not shown in all_composite_ids (or available_composite_ids either); previously it was.

• Closes scene.available_composite_names() return a composite even the dependency is not fullfilled #853
• Tests added and test suite added to parent suite
• Tests passed
• Passes flake8 satpy
• Fully documented

[coveralls]

Coverage increased (+0.03%) to 85.378% when pulling ee9a108 on djhoese:bugfix-available-composites into 95b0aea on pytroll:master.

[pnuu]

Just few comments.

[yufeizhu600]

I have tested the PR, it works as I expected now. Thanks.

[sfinkens]

I'm still struggling with this part of the code, but these changes make it more clear and thanks to all the new docstrings it is easier to understand now! 👍

[mraspaud]

Quickly tested with modis data, nothing bad to report. LGTM.