Add: Now sphinx executable can be selected by the user from file system.
Add: Sphinx executable will be checked by the setting widget.
Add: Sphinx output extension can be selected from drop down menu (only html or htm) or can be defined by the user (any extension. But in basic setting mode the actual sphinx builder will still be html).
Fix: Cleanup setting widget tabstops.
Todo: Test cases for thoes 2 added functions.