feat: keymaps for color selection (#251)

[freddiehaddad]

This commit adds the following keymaps:

• P: toggle the color palette UI
• 0: select palette color 0
• 1: select palette color 1
• 2: select palette color 2
• 3: select palette color 3
• 4: select palette color 4
• 5: select palette color 5
• 6: select palette color 6
• 7: select palette color 7
• 8: select palette color 8
• 9: select palette color 9

If there are fewer than 10 colors in the palette, keymaps for colors beyond what's in the palette will result in selecting the last color. For example, if there are 3 colors in the palette and the user presses 4, then color 3 is selected.

For palettes with more than 10 colors, manual selection is still required for colors after 10.