Implements multiple objects detection

WIP, untested

Conflicts:
	blort_ros/src/nodes/learnsifts.cpp
BOD

Partial tracking of multiple objects, WIP, does not compile
Implementation of multi-objects tracking

Compiling, to be tested...

Conflicts:
	blort_ros/src/nodes/tracker_node.cpp
Fix segfault when training

No model  was loaded hence  no model  existed and segfault  occured when
trying to learn new sifts
Don't draw models that are not currently tracked
Remove deprecated function
Publish object name too

Conflicts:
	blort_ros/src/nodes/tracker_node.cpp
Split declaration/implementation for TrackerNode

Conflicts:
	blort_ros/src/nodes/tracker_node.cpp
Execute recovery calls in a separate thread

This allows to keep tracking currently tracked objects while looking for other
objects.

ToDo: launch recognition for multiple objects at a time.
Recover multiple objects simultaneously

Conflicts:
	blort_ros/src/gldetector.cpp
	blort_ros/src/nodes/detector_node.cpp
Properly handle image encoding in detector node
Enable object selection for detection

ToDo: use in the ROS node

Conflicts:
	blort/src/Recognizer3D/Recognizer3D.cpp
Use select recognition in node

Conflicts:
	blort_ros/src/gldetector.cpp
Prepare tracker service for multiple params
Possibility to reset tracking on an per-object basis

Conflicts:
	blort_ros/src/gltracker.cpp
Add a call to switch tracking on/off for certain objects

Conflicts:
	blort_ros/src/gltracker.cpp
[TMP] Draw even in poor quality

This is necessary during training but should be disabled afterwards
Fix getter/setter for PublishMode

-> Rename setPublisMode to setPublishMode
-> Add a getter

Conflicts:
	blort_ros/src/nodes/tracker_node.cpp
Fix minor issues for pull request
Fixes identation issue and default model