Confusing variable access in imageCallback() and poseEstimateCallback()

[fmros]

Problem

There are variables like corners or ids accessed in the imageCallback and in the poseEstimateCallback method that are not protected for race conditions. Allthough there is no parallel execution of the threads specified through e.g. MultiThreadedSpinner, i think these variables should be accessed through the incoming message in the poseEstimationCallback and not through the private class members.