Feature: more configurable colours

[jernejs]

Right now highlighting lets you configure background colour only, and Process Hacker automatically chooses text colour - it'd be nicer if both colours were configurable (I use Windows in High Contrast mode, but with customised colours to have a low contrast dark theme, and white text colour that PH selects for dark backgrounds is too bright for me).

There's also a problem on the Firewall tab, where text is black, while Windows default background is used, which makes the text invisible (and a related issue in the System Information window, where the inactive buttons on the left have white background).