Reorganized DimLink Code

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.
Progress on Rewriting Packet Handling

Continued building a system for transferring the complete internal
states of our dimensions from the server to the client. However, Steven
suggested that clients only need minimal data to operate properly, as
opposed to the server. My motivation for this more complicated system
was the concern that minimal information wouldn't be enough. I'm going
to commit my progress, then tear it down and write a much simpler
version.
Overhauled Server-Side Packet Handling

Threw out the complicated architecture that I'd made for synchronizing
server and client data perfectly. Instead, we now send just enough data
to the client and the resulting code is simpler. Some of the client-side
code is also done so all packet handling should be finished soon.
Completed Packet Handling Code

Finished implementing all the packet handling code. It could be improved
in the future to compress the initial packet sent to clients. With this,
the code is complete enough to run! Commands have not been fixed yet but
that will come in the future.
Fixed Bugs

Fixed bugs that would cause Minecraft to crash on startup. At least I
can get to the main menu now.
Fixed More Bugs

Fixed more bugs. Now it's possible to generate a world without crashing.
Unfortunately, it's clear that there is a packet-sending loop going on.
I'll have to add a check to prevent integrated servers from spamming
themselves.
Minor Changes

Minor changes: removed unused imports and random blocks of whitespace
Fixed More Bugs

Fixed the issue with integrated servers causing circular updates between
the combined server and client. We now check on the client side whether
the connection we're receiving data from is a memory connection (which
is presumably only used by integrated servers). If so, the client
ignores any incoming packets. We don't just disable update events
altogether because LAN games will require updating remote clients.

Also fixed a bug in PocketManager.unload() - we weren't setting isLoaded
to false after unloading everything and unregisterPockets() had to be
called before setting dimensionData to null.
Merge pull request #81 from SenseiKiwi/rewrite

Rewrote All the Things