New Plugin detection method

Implemented new method to detect plugins and themes.
Now only the foldername is checked instead of a particular file.
This should fix Issue #111 where older plugins are not detected because of missing files in older versions.
On my tests all Blogs returned a correct status code on the directory itself but i want to provide it as a pull request to get your feedback too.
I also updated the data files.

PS: If a plugin was only in plugin_vulns.xml but not in plugins*.txt, there was also only a check on the directory itself