explorer: paint feature highlights via ev_get_bg_color hook

[williballenthin]

example here: https://github.com/williballenthin/idawilli/blob/1d3bbee0bbf12440cdaac4dacecf8021d5d5fe4f/plugins/colors.py#LL13C8-L13C24

benefits:

• we don't change the opened database, which helps when sharing the IDB elsewhere
• we don't have to clean up the colors when we're done running, or try to track state of each address

[ghost]

Hi Willi, would it be okay if I try my hand at this?

[williballenthin]

of course, that would be great!

feel free to take a stab as you see fit and/or propose a strategy here and/or ask any questions you may have. we're here to help.

[ghost]

Great! I will try to work on it this weekend. Thank you. :)