Add more color variables

[costateixeira]

Add color variables for:

• Breadcrumb font
• Footer font
• Dragon background
• Dragon font

[ElliotSilver]

See #117

[ElliotSilver]

Helpful variables include:

• body text, heading text, and background colors
• publish box text, link, and hover colors
• table of contents text, link, hover colors
• STU note text, link, hover colors; and STU "headline" text and background colors
• dragon box border, link, hover colors
• footer nav text, link, hover colors
• breadcrumb separator color (for the >)
• button text color for hover, active, dropdown, dropdown hover

I haven't investigated, but note-to-balloters probably needs variables too, as well as any other new styles that we've defined.

Ideally, we should find a way for colors to flow from one variable to another to mimic current behavior (i.e. most of the link colors should "inherit" --link-color unless overridden)

Once done, update the IG Guidance color page to list the new variables in the text and diagram.

[ElliotSilver]

Also, publication status box (colse, colsdp, colstu, colsd, colsi) text, background, border.