Max marker setting even counts markers that are off

[corneliusroemer]

To keep the UI smooth, we disable marker preview when there are too many markers.

When trying to view a sequence with many N ranges but few mutations, I expected to be able to just switch off the display of N ranges and then be able to get below the marker limit.

Unfortunately that didn't work!

With those settings:

I still get hidden markers:

There are two ways forward:

• quick: rename the "Max nucleotide markers" to "Maximum markers (including hidden)" (the mention of nucleotide is wrong here, as all sorts of markers are counted not just nucleotides)
• Improve visibility business logic to only count enabled markers towards the threshold