Create the new types enum.

This is really important. Please please review. 
Give a "ship it!" if you're happy with the enum. I will only push into the model_refactor_3 branch.

Obviously this won't compile, I want to make sure people are happy with this _before_ we start changing all the other code. We can add roles later, but I don't want to be editing or deleting them. 

I'm also not sure whether I should namespace the enum so we don't have roles at the top level of the KTp namespace?  (i.e namespace KTp { namespace ContactModelRoles { enum ModelRoles{ .....  ) ? Thoughts?

(what's not shown in the diff is that I've also deleted/merged the ktp-metatypes.h file)