Imu Controller Spike

This is really just meant to be a spike to try some things out for the IMU/Accelerometer with separated controllers. I haven't extended it to Temperature or Gyro because I wanted to get some feedback first.

There is a controllers service which is responsible for mapping controllers on boards. There are two controllers implemented in this pass: AnalogAccelerometer and MPU6050. Thy both expose data.accelerometer[x,y,z] data points, but they get the data in different ways.

I tested this with an analog Accelerometer as well as with the MPU-6050.
Ok, I get this organization, but it's still at odds with what I'd like to see. This `AnalogAccelerometer` doesn't need to be its own file, and neither does the Accelerometer-specific "pseudo controller" (quotes because it's really just emitting from the actual MPU6050 controller, so therefore not really it's own controller). 


In `lib/accelerometer.js`:

```js
var Controllers = {
   ANALOG: {
   ... all the stuff for an analog accelerometer
   }, 
   MPU6050: {
     initialize: function() {
       ... get the active MPU6050 controller or initialize it. Do stuff. 
     }
   }
}
```