esx: Generate most SOAP mapping and improve inheritance handling

esx: Generate most SOAP mapping and improve inheritance handling

The Python script generates the mappings based on the type descriptions
in the esx_vi_generator.input file.

This also improves the inheritance handling and allows to get rid of the
ugly, inflexible, and error prone _base/_super approach. Now every struct
that represents a SOAP type contains a _type member, that allows to
recreate C++-like dynamic dispatch for "method" calls in C.