Fix Issue #1167, Fix Issue #1161, Ignore MacOSX hidden files

Adjust two places where the ```.value()``` function of a QSettings item is called, including the argument ```type = 'QString'```, rather than letting it default to ```None```. On my installation (Mac OS X 10.8), it had returned a QVariant object instead of a string, as is expected by the program usage. I also changed the usage so that it calls the function with keyword arguments rather than position, for better readability.

I also added .DS_Store (a file added by Mac OS X to save folder view options) to the list of git ignored files.