New training forestry module

rst files and images added for first time
thanks for the tips Tim.
About the version to which this applies, I remember (maybe wrong) that it was valid for 2.4. too... But it also might vary from mac/linux/windows versions... that's why I leave it like "if you find a folder named so" just delete it... if no folder, then do nothing :). I will review it for 2.6. too. The instructions then use that same folder for extracting the up2date provided folder... this is valid for 2.4 too (tested on windows)... but I will keep a close eye to see how these instructions are valid for 2.6, since situation may change.