Add the ability to configure cameras

[curtiswest]

The current implementation of PEPI does not support camera configuration.

If multiple cameras are used, it may be advantageous to be able to configure their parameters, e.g. white balance, exposure, ISO, etc. to achieve a consistent capture.

This enhancement proposes an extension of the CameraServer defined in pepi.thrift called ConfigurableCameraServer. This would take the form of:

service ConfigurableCameraServer extends CameraServer {
    i32 iso(1:i32 value),
    i32 white_balance_temp(1:i32 value),
    float shutter_speed(1:float value)
}

There will need to be some thoughtful consideration put into deciding which operations to include in this new extension. Additionally, will need to look into some mechanism whereby server access will fallback to a normal CameraServer if ConfigurableCameraServer is not implemented. Such a mechanism may already be available in Thrift?

The user interface will need to be updated to accept these configuration functions.