add processor_capture_holder

Add a processor which sole purpose is associate a capture of any type to a key-frame creation.
The processor keeps a time-windowed list of CaptureBasePtr from any sensor, on the keyFrameCallback it associates the closest capture it holds to the key-frame.

This can be convenient in situation such as :
A laser sensor is used as the main odometer through ICP. Its CaptureLaser are transformed into CaptureMotion within the processor getIncomingCaptureMotion function. Thus there is no laser anymore to build any map representation from the lasers. This processor aims at 'keeping' the scan for later map construction.