Update issue #65 : Don't place filters higher than the first downstream filter which has already been positioned or any intermediate columns
Adds a bit of space vertically decreasing chances of connection lines crossing filters and makes structure of graph a bit more visible.

git-svn-id: http://graph-studio-next.googlecode.com/svn/trunk@148 c2f33eb2-41b2-391d-4cb4-d9d0608729ba