Move old unit tests for Source
Add assignment operator for nullptr_t to Source

Add missing operator<< to Source
Method testOperators was not registered on TestBlock
Started unit test for nix::Source
Add missing implementation for Source::sources()

Harmonize some implementations of other methods of SourceHDF5.
Remove TODOS and commetnted code parts.
Unit test for nix::Source done
Implement method findSource
Some changes according to the comment of @gicmo
Merge pull request #47 from stoewer/master

Unit test for nix::Source

Fixes the Source part of the unit tests meta-issue #25.
Reviewed and tested locally.
Move old unit tests for Section
Remove outdated comments
Add missing operators to nix::Section
Create basic unit test for nix::Section
Make acceptAllFilter() a template and move to util
Implement section access methods for Sections
Remove tnode because it is no longer needed.
Implement accessors for propertis on sections
ImplContainer: fix constness of operator== and operator!=
Section: the property link now handles Sections

File: add findSections method and remove old one
Section has now a working getter for parent