Fix Compiler Warnings

Fixes compiler warnings produced during build of the GUI app.

Changes:

 * src/GUI/data_access.cpp: Fix warnings related to passing QString
   objects to qWarning, which expects C strings.
 * src/GUI/combine_perfReses_dialog.cpp: Fix warnings related to the
   use of string constants by casting them to char *.
Convert Calls to latin1 to qPrintable

Adds code to convert all the remaining calls to the qPrintable macro
instead, since it's more flexible and cleaner.

Changes:

 * src/GUI/combine_perfReses_dialog.cpp
 * src/GUI/data_access.cpp
 * src/GUI/data_table.cpp
 * src/GUI/pt_main_window.cpp
Change fprintf to qDebug et al. When Appropriate

Changes the fprintf calls in Qt code to qDebug, qWarning, etc. to be
consistent.

Changes:

  * comb_perfRes_widget.cpp
  * pt_main_window.cpp
  * tg_barchart.cpp
  * data_access.cpp
  * data_table.cpp
  * main.cpp