Fix opening of GUIs (with client/server sync) and fix Knapsack gui.

This:
* Fixes GUI opening code (In my previous pull request I only opened it client side)
* Actually sends packets of other events and syncs client and server NBT data on connect. (well, it would if it weren't for MinecraftForge/FML#381 which doesn't fire PlayerLoggedOutEvent). A workaround is to go to the nether (to fire onPlayerChangedDimensionEevent).
* Fixes the background of the knapsack GUI so it is in the correct spot.

![armorguifix1](https://f.cloud.github.com/assets/339225/2269659/0f01bcb2-9ede-11e3-8da7-2d442faa278c.png)
![armorguifix2](https://f.cloud.github.com/assets/339225/2269660/0f4f0396-9ede-11e3-8f97-110603f352ac.png)