Find plugin directory.

Still to do:
* go up till eclipse directory
* look for swi/yap
* if not exist -> do the same like before
Automatically find locally installed Prolog version (parentFolder of eclipse/prolog/swi).
added legend for graphical views
comment regarding linux and the installer
Merge branch 'internal_prolog_version'

Conflicts:
	pdt.connector/src/org/cs3/pdt/connector/internal/preferences/PreferenceConfiguration.java