add natural sort - issue #124
removed unneeded print statement
Natural String should inherit from str - issue #124
Removed superfluous variable _string and tidied up the NaturalString class a little
Merge branch 'master' of https://github.com/fossfreedom/coverart-browser into naturalsort
Merge branch 'naturalsort' of https://github.com/fossfreedom/coverart-browser into naturalsort