[BUG-178] Refine Unhardcode all XDG standard paths code a bit;

[brezerk]

Changes:

• Update corelib path* functions to produce cross platform output;
• Fixup wrong string text placeholder;

Address: #178

[brezerk]

jfyi: @gasinvein btw: if you would like to add something to https://github.com/brezerk/q4wine/blob/master/AUTHORS file -- let me know;