merge: refactor colour handling / notifications

 * rename and reorder color constants
 * tidy whitespace
 * rename vars
 * convert retval to CommandResult
 * tidy code
 * rename/move function
 * do_uncolor change param to retval
 * encapsulate all the colours
 * fix max quote depth
 * encapsulate defs
 * encapsulate quoted
 * encapsulate color_list
 * move mutt_color_free
 * move parse_object
 * initialise lists
 * move color_line_new
 * move mutt_colors_free
 * deglobalise Colors
 * implement more uncolor commands
 * colour notifications
 * sort symbols
 * docs: color/uncolor