Merge pull request #14 from NLeSC/feature/ssh-adaptor-3

Feature/ssh adaptor 3
Completed RelativePath implementation.
Merge branch 'develop' of ssh://github.com/NLeSC/octopus into develop
Added copy constructor to RelativePath. 
Added constructor to AbsolutePathImplementation that accepts multiple
RelativePaths.
Merge remote-tracking branch 'origin/develop' into feature/ssh-adaptor-3
Renamed credential implementations.