feat: global color palette

[batonac]

A global color palette would greatly enhance the builder experience and design management capabilities.

A few suggestions:

• Add a "Site Colors" global config pane to the "Settings" panel in the builder UI, similar to Cwicly:
  

• Add a color selector popup which allows for manual color mixing or selecting from a global color variable, similar to Cwicly:

• Integrate with the planned Variables for style & properties

• Integrate with Frappe core "Color" doctype.

• Integrate with the Frappe core "Website Theme" doctype to allow for default primary/text/light/dark color assignment from the "Settings" panel (unless this is being totally deprecated).

[batonac]

Edit: I should have acknowledged that the color selector popup exists already and is off to a great start, but would ideally allow for selecting from a global color variable list, not just hex values of recently selected colors.
Edit edit: the current color selector is hard-coded, not even recently selected colors. Bummer.