Registration admin color-coded sections/buttons

[kr-matthews]

My intention was to change the yellow color (since contrast isn't good enough with white text) and improve the button UI on mobile, but then this happened. I'll improve the buttons next.

• Reorder action buttons to the same order as the tables.
• Adjust the colors (and some icons) of these buttons.
• Add colors to the tables & section headers too, to make it easier to find sections at a glance, and to easily see which table you're in mid-table.
• Disable the missing button instead of hiding it, when only 1 registration is selected.

These are the available colors. I didn't use brown because the light version (which appears in the left column of the table) looks the same as the light version of orange.

If the section headers are too much, then just coloring the text is another option. Or keeping them black, but then you can't see the color at all when collapsed.

It's also possible to color the entire table, but I think that's way too much:

Preview of next PR - grouping action buttons into a dropdown:

[gregorbg]

I love it! As far as my personal taste goes, I think coloring the headers is a bit too much. But I definitely want more opinions on this change, as this is not a matter that I have "jurisdiction" over. (But I do agree that fully coloring the tables is way too much 😂 )