wiki/_license/*/: symlink the contents instead of the folders, because the root dir's and wiki's applies_to.txt's will be different

wiki/_license/LICENSE.TXT: replaced with README.TXT as in /_license

added wiki/LICENSE.TXT,_license/, with license terms that apply specifically to the wiki (which is BSD, not GPL). note that the wiki attachments are NOT open-source, only the page text.