Merge branch 'master' of https://github.com/G-Node/pandora
new tree_depth method in Section that gives the maximum levels below a
section
implemented Section::findDownstream(type) that is needed to find
related sections
implemented Section::findUpstream(type) helper function needed in find
related.
implementation of Section::findRelated(type) done!
result checks introduced because Section::findSection includes itself
into the search results.
Checks may be removed if we decide to exclude the starting section
from findSection
docstring  of Section::findRelated, and remove of old hasRelated
method stub