Add navigation type to IRequest.

OnBeforeNavigation was deprecated in CEF and OnBeforeBrowse has not navigation type parameter anymore. So there is no way to get this info now. In this feature navigation type added in request interfacce accordingly CEF.
Few things with this one
- Rename to `TransitionType` to match `Cef` api
- Include `Xml` doco for each value as per http://magpcss.org/ceforum/apidocs3/projects/%28default%29/cef_transition_type_t.html
- Separate file (including license agreement), see `KeyType` for example.