Add options to load automatically the more recent grib file in the default directory or the last  previously loaded
Refactoring: fixed some wxString parameters which were not const references. Also some methods are now const that weren't.
Retained compatibility to plugins after refactoring of the const wxString references as method parameters.
Merge pull request #59 from Ptizef/master

Add options to automatically load the more recent grib file in the default directory ot the last previously loaded
Make grib change columns to better use space
Merge pull request #61 from mariokonrad/refactor

Refactoring: method paramters: const references of wxString instead of call by value, keeping binary compatibility with existing plugins.