Support setting specific bits of multi-bit components

[dkilfoyle]

Currently the only way to set a specific bit for a multi-bit component such as a register is to rewrite the entire value

myRegister = 3; // will set my register to 0b11

Need to implement ability to set specific bits such as

myRegister[1] = 1;

This should only be allowed for components where setting a specific bit makes sense = registers, multibit buffers/wires.

This will be best accomplished by refactoring "gates" into component class hierarchy:

1. Component {state:Numeric, inputs:[], update(), setValue(), getValue()}
   1. Gate extends Component {logicFn: and, or etc, function in update}
   2. SevenSeg
   3. Number
   4. MaskableComponent { inputMasks: [] = which bits the input contributes to, setValue(x, mask), update calls setValue for each input }
      1. Register
      2. Wire