Project restructuring

There are still some issues to be resolved on the branch. Some additional suggestions are:

• The hyperparameter likelihood isn't really a GW thing, it probably doesn't belong in the core either.
• The default functionality in prior should be in GW.
• The test_redundancy should be in GW.
• I think references to injection_parameters in core should be changed to true_parameters for generality.
• Result.construct_cbc_derived_parameters should be in gw/conversion, this is something I think I put in the wrong place.