Trajectory improvements

Improvements ideas from #9:

• Add inc_ca, emi_ca, phase_ca to Flyby object.
• Split MaskedTrajectory into MaskedSpacecraftTrajectory and MaskedInstrumentTrajectory
• Add fovs to MaskedInstrumentTrajectory
• Add facecolors and edgecolors keywords arguments on .fovs() similar to Trajectory display property (e.g. inc).
• Add manually a colorbar to an axis with a known extent and a custom colormap.
• Add fovs sorting attribute.
• Update the examples and the docs.