[ctest] Add ctest continuous integration script for unix

Use with ctest [-V] -S.unix.ctest
[travis] remove old and obsolete travis file for osx [ci skip]
Merge pull request #90 from balint42/master

updated "contributing" doc
Merge pull request #98 from jgrewe/master

Getter of optional fields return boost::optionals
Closes #86 

Looks good to me!
Merge pull request #99 from balint42/master

removed "findEntities", completed use of "getEntities" & removed "children" methods
Merge branch 'master' of https://github.com/jgrewe/pandora-1
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
using filters for find related
changes related to gicmo's comments i.e. checking string equality with
== instead of using compare, using it->id() rather than (*it).id().
Merge pull request #107 from jgrewe/find_related

Implemented findRelated Sections functionality in Section

LGTM