Observer implementation

[BramOtte]

It seemed like a relatively simple redstone component and I wanted to implement one :D.

Observers are however a bit different to other redstone components as they react to any state change of the block behind them instead of responding to absolute redstone signals.
The observer should also only respond to the block it is looking at for this a few changes need to be made that allows the block to see where the updates come from.

A few notable things that update observers are:

• all sides of redstone including the top
• all sides of repeaters, comparators and other observers
• locking repeaters
• torches
• redstone lamps, trapdoors
• buttons, levers and pressure plates