[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/capture_base.cpp

@@ -3,7 +3,7 @@
 
 namespace wolf{
 
-unsigned int CaptureBase::capture_id_count_ = 0;
+std::atomic_uint CaptureBase::capture_id_count_(0);
 
 CaptureBase::CaptureBase(const std::string& _type, const TimeStamp& _ts, SensorBasePtr _sensor_ptr) :
         NodeBase("CAPTURE", _type),