[WIP] ProcessorBase multi-threading

[WIP] Depends on !89 (merged) .

Add a ThreadedBaseClass that ProcessorBase inherit from.

It allows the computation of the ProcessorBase::process(...) to be performed in a separated thread. Threads aren't instantiated/killed but instead are put to sleep waiting for new CaptureBase.

ThreadedBaseClass API is rather simple :

• Constructor with argument max_frequency allowing the user to set guess what, a max frequency at which the processor operates.
• run() to start the thread and so the processor.
• stop() allows to stop the thread and so the processor.
• isRunning() let the user know if the processor is running or not.

Finally it has the pure virtual function :

• executeImpl() where the derived class do its job.

src/sensor_base.h

@@ -162,6 +162,7 @@ inline ProcessorBasePtr SensorBase::addProcessor(ProcessorBasePtr _proc_ptr)
     processor_list_.push_back(_proc_ptr);
     _proc_ptr->setSensorPtr(shared_from_this());
     _proc_ptr->setProblem(getProblem());
+    _proc_ptr->run();
     return _proc_ptr;
 }