Add foreground colour to mark-all etc

[majenkotech]

Some colouring options, such as Mark All Occurrences, only allow you to colour the background of the text, and not set the foreground colour. This really restricts the range of colours you can use in the highlighting, as you can't set a good contrasting colour for the foreground to be able to read the text with some background colours.

This is seldom a problem with dark-on-light themes, but when you have a light-on-dark theme it is hard to get a bright highlight colour that also allows you to read the light coloured text, so it would be good to be able to change the foreground colour to a dark colour for the lighter highlight.