File writing, start of mods

The write file is quasi-stable now.
What I've also done is start the basics for modding. It isn't functional yet, but people might want to look at it.
The idea is we define an interface (IBlocksPlugin). People write mods to that interface, put them in a jar, put a reference to each of their mods in the MANIFEST.MF, and then drop the jar into a subdirectory off of StarMade. Any tool using them looks there and dynamically loads them.