[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/CMakeLists.txt

@@ -177,6 +177,8 @@ SET(HDRS
state_quaternion.h
time_stamp.h
trajectory_base.h
+    threaded_base_class.h
+    multi_threading_utils.h
)
@@ -240,6 +242,7 @@ SET(SRCS
sensor_odom_3D.cpp
time_stamp.cpp
trajectory_base.cpp
+    threaded_base_class.cpp
data_association/association_solver.cpp
data_association/association_node.cpp
data_association/association_tree.cpp