Add event detectors

[astrojuanlu]

• Next ascending/descending node (for orbit counting)
• Next latitude peak (for alternative orbit counting)
• Next eclipse (or penumbra) start/end

And then some events already buried in LocationPredictor, like:

• Next time of closest approach (TCA) over location
• Next AOS/LOS over location with given conditions (minimum elevation at AOS, minimum max elevation, illumination on satellite)