Implement Boore, Joyner and Fumal 1993 GMPE for 2010 Western Canada Model

This pr implements GMPEs needed for the implementation of the 2010 Western Canada Model (https://bugs.launchpad.net/oq-hazardlib/+bug/1266790).

For the moment test data have been generated from the hazard lib implementation. As soon as I receive test data from the original authors I will update the tests