Added from-python conversion of RunTimeTypedClass to IECore::TypeId.

This makes calls to things like RunTimeTyped.inheritsFrom() a little more Pythonic, without littering staticTypeId() calls all over the place. The main motivation for this is to replace the isolated code from here :

https://github.com/ImageEngine/gaffer/blob/master/src/GafferBindings/MetadataBinding.cpp#L114

This will allow us to make the Gaffer API more consistent - currently most registration functions implemented in Python take classes directly, but those implemented in C++ and bound to Python require TypeIds. Accepting classes everywhere will make the API simpler and more uniform.
Removed implicit surface functionality.

This hasn't been used in production for a long time, and is considered superceded by functionality elsewhere, in particular OpenVDB.  I've kept the files in the repository for now by just moving them to the contrib directory, so they can be found easily by interested parties if they'd like to use/copy/study/fork it.
Merge pull request #288 from johnhaddon/typeIdBinding

Added from-python conversion of RunTimeTypedClass to IECore::TypeId.
Merge pull request #289 from johnhaddon/implicitSurfaceRemoval

Removed implicit surface functionality.