Remove dir from OutputManager

The output manager takes a directory as an argument as well as a file name and simply appends them together. The default dir (and what is currently in corsika.cpp) is the $PWD. So you effectively cannot make a shower in another directory. This seems bad to me because it means you cannot be in directory X and write to any directory that isn't a sub-dir of directory X.

Normally, one would simply pass in the full path to where they want to write and not need a pre-directory.