Moved the DimLink code out of NewDimData in order to reduce clutter
inside that class and made it a separate class, except for functions
that should only be available for NewDimData. Deleted IDimLink and
changed all references to it to use DimLink instead. DimLink is now an
abstract class, which achieves the same encapsulation and protection we
had before by having DimLink implement IDimLink from within NewDimData.
NewDimData has a new class inside, InnerDimLink, which provides it
access to special functions that would be dangerous to expose. This is
the same mechanism used to protect NewDimData's dangerous functions.
These changes are in preparation for adding more code for packet
handling.
Started rewriting our packet handling code. Deleted PacketHandler in
favor of using sided (Server-, Client-) packet handlers to make it
easier to follow what's going on in our code. Added some event-based
handling of updates which greatly simplified signaling that data needs
to be sent, but it's not completely done yet.
Modified how links are created so that the caller must specify a link
type when the link is created, rather than setting it later. This was
done to avoid having to send two link data packets following the way
links would be handled logically. Turns out this was good idea overall
for ensuring link integrity, because there was one case where I forgot
to set the link type after creating the link.
