feature request: max magnitude of dsos

[fommil]

Suggested in #22 but pulling it out as its own feature.

It is currently possible to limit the stars and (all) DSOs by magnitude, but I'm interested in limiting stars (mag_max) and each DSO type independently. This would make for very useful and uncluttered star charts for visual observing.

I see there are DSO classifications for

• Galaxy
• Bright nebula
• Open cluster
• Globular cluster
• Planetary nebula

so having a max magnitude for each of these would be perfect, and also a way to force them to be labelled! (I can provide my own labels like in the referenced ticket but having this out of the box would be perfect).

[fommil]

I should clarify, I don't mean this setting, this is applied to DSOs of all types

dso_mag_min=10

I was hoping for something that applies to each kind of DSO. And similarly, for the dso_label_mag_min to be applicable to each of the types of DSO.