Colorbrewer palettes not using correct default number of colors

[Elaine Meng]

Currently the documentation for using Colorbrewer palettes in ChimeraX says they have default numbers of colors.

That is, each palette has an initial name optionally followed by -N where the N is the number of colors to use. If the "-N" part is omitted, then the default number of colors is used, and according to the documentation default N is:
6 for qualitative palettes
5 for sequential and diverging palettes

<​https://rbvi.ucsf.edu/chimerax/docs/user/commands/palettes.html>

However, tests by me and Eric in the daily build show that when the -N is omitted, you always get the smallest possible version of each palette (3 colors).

This is highly reminiscent of the new colorname-parsing error that appeared since the 1.1 release, #4208.

[pett]

I feel that these color-parsing bugs should be fixed before 1.2

[pett]

This bug is also fouling up my Color Key tool. For the 6-color case, the tool know that "pastel1" is an applicable palette name, so shows it in the available-palette menu. If the user actually tries to use it though, the tool runs this command:

key pastel1 :min : :max : : :

which due to this bug is expanded to:

key pastel1-3 :min : :max : : :

which fails because 6 labels are being specified for 3 colors.

[Greg Couch]

The fix for #4208 appears to fix this too.

key pastel1 :12 : :24 : : : is now the same when expanded.

color seq res pal paired appears to work correctly too.