fix #166 part1/2: define SLCONFIG char* initializator

Using _T() inside the SLCONFIG macro messes stuff up
the better way is to provide an initializer for char*
inside the initializer the conversion to wxString occurs.
fix #166 part 2/2: use right form of Read()

wrong signature:

  const wxString Read (const wxString &key, const wxString &defaultVal) const

right signature:

  bool Read (const wxString &key, wxString *str) const

the wrong one returns the red value, and takes second parameter as
default value. The right one takes pointer to value and modifies it, if
a value is present.