pre-process incoming CaptureBase to CaptureMotion

Add ProcessorMotion::processIncomingCapture function.
Called at the very beginning of the process scheme, it converts the input CaptureBasePtr (_incoming_ptr) to a CaptureMotionPtr. The default implementation remains exactly the same while allowing derived classes to overload the newly added processIncomingCapture function.

Use-case :
A Scan-matching-based ProcessorMotion receives a LaserCapture. It thus has to compute the actual scan-matching in order to estimate a MotionCapture. It therefor takes place in processIncomingCapture.
While this may not be ideal, it is the simplest/easiest hack around this problem.

Note, I thought I had added this a while ago, maybe not.

src/processor_motion.cpp

@@ -46,7 +46,14 @@ void ProcessorMotion::process(CaptureBasePtr _incoming_ptr)
         return;
     }
 
-    incoming_ptr_ = std::static_pointer_cast<CaptureMotion>(_incoming_ptr);
+    incoming_ptr_ = processIncomingCapture(_incoming_ptr);
+
+    /// @todo Anything else to do ?
+    if (incoming_ptr_ == nullptr)
+    {
+      WOLF_WARN("Processor motion received a nullptr incoming_ptr_.")
+      return;
+    }
 
     preProcess(); // Derived class operations