Feature/runtime defaults

Runtime Default Feature.

I accidentially pushed two commits to master before merging, to comment on them see the following urls:
https://github.com/dkunzler/esperandro/commit/4e8eb782d2b4ee4a591d3e7c0e22a67e382184c5 (unit Tests)
https://github.com/dkunzler/esperandro/commit/66c54b38baf5fd4d728665ba5c91f0a684bab864 (check for potential getter accepts runtime defaults)