This patch is done in the context of TileLibrary synchronization and RPC
implementation.

Through the process of implementing RPC, a intrusive simplification in the
network message system has been implemented, completely removing the use
of PayloadArray. On top of that, ClassMapping is now much more flexible,
and doesn't need to be provided with a static size anymore, making it closer
to a suitable class for the needs of RPC message passing.

The result of this simplification is also a slight optimization of message
passing, where certain data needed to be passed over the network (for example
on null objects) which is not needed anymore.

With regards to the TileLibrary itself, the implementation is yet pretty
basic, showcasing the use of RPC to retreive a list of strings computed on
the server.