Move to one jar for distribution

This PR adds a lot of things:

- Some classes are now shared between the client and the server. (com.forgeessentials.commons package)

- The servercomplete will no longer be distributed as a zip for extraction, it is now distributed as a single jar containing all modules (including WEIntegration!) and all dependencies. Use main.cfg to disable modules.

- We now include WorldEdit 6 in the official FE distributable. It will be extracted to your mods folder, where you can replace it with a newer version from sk89q.com if you like.

- Libraries will also come with the FE core jar, and are extracted at startup.

**NOT** to be accepted until I give the go ahead, as Jenkins has to be reconfigured.

Merging this PR will resolve #1050