#3 support file type detection

[J.Guillaume (ioguix) de Rorthais]

Gisx should be able to know the type of each files.

It is firstly needed in ListView to print the file type in the "Type" column instead of just "Répertoire" or "Fichier"...

Then, it will be needed in future in the Viewer and ThumbView to know how to show the wanted file/Thumb (text, picture, ...)