Initial geoadmin3 structure

As discussed yesterday.

- Minimal buildout-based setup of geoadmin3
- Does not contain pyramids/papyrus
- Purely static configuration
- Git submodules are placed into third-party directory (contains ol3 at the moment)
- README.md contains steps to get started (boostraping, buildout, configuration)
- Structure should be in the way to allow easy merging of existing branches

Todo (probably Tom):
- set up buildout steps to build ol3 and create symboly links into geoadmin/static directory