[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