Abstract away from just about everything

[DaMatrix]

This is a huge PR (which, in retrospect, probably should have been broken up into multiple smaller PRs). In combination with #117, it makes the vast majority of the codebase be able to operate entirely independently of the Minecraft version being used.

Additional major changes include:

• The tile size for heightmap and voxel modes are now separate. The replacements for T_SHIFT and related constants are now to HeightmapConstants/VoxelConstants
• The makefile-based system for compiling native code has been replaced with a Gradle plugin. This should make future changes substantially easier.
• GUI code is completely rewritten.
• All of the static event handler classes have been replaced with a universal FEventBus, which uses a familiar annotation-based event subscription system. It supports a few additional features not commonly found in other event buses, such as the ability to weakly reference a registered handler object, and generic parameter matching.
• The @DebugOnly annotation is now gone. Debug statistics and related features are now available outside of debug mode.
• Logging is now routed through a PorkLib Logger, as are messages which appear in the client-side chat menu.

With the exception of the :gl module and children (which are handled by #117), nearly everything is affected in some way.

Known shortcomings:

• GPU frustum culling will currently crash on heightmap mode.

[nickcat325]

I've tested this and it works well. You should mark this for review.

[DaMatrix]

there is still some work required before i can merge this: most importantly, i need to make heightmap mode actually work with the abstracted API, which i'm currently doing on dev/abstract-heightmap-gen.

once that's done, i also still want to do a last round of refactoring in order to minimize the amount of duplicated code between versions, and move more stuff to the :api module to make it more useful.