Move CustomerFwd behind Customer

All the previously-lazy BackendSgx data is now either all loaded or all not
loaded by swapping the sgx_repo used by your CustomerRepo instance.  When not
loaded the fields are filled with bottom values that explode when used.  When
loaded the values are present in RAM and not promises at all.  Most code paths
do not need any of the data, a few need most of it, so this seems like a good
trade-off.  Most code using this object will simply never touch those fields or
care about how they are loaded, etc.

Of course, most of this data isn't even SGX related and should move out of here,
but that would take a data model refactor/migration on the catapult_* schema.