Allow setting background and text colors of Treelist items

The changes included enhance the Treelist with the ability to set the text foreground and background colors on individual rows of the list.  The colors can be set/unset using the standard MC_TLM_SETITEM message.  There is a BOOL for each (text and background) indicating whether a custom color should be used at all and a DWORD containing the RGB value of said color.

I had a need for this functionality in one of my projects.  It may be useful to others, but I do realize that it deviates significantly from, for example, the standard Win32 ListView.  If you think its worthwhile, it might be a nice enhancement for mCtrl.