Blob detection nodelet

[HuiShiSerenaShi]

Hello, opencv_apps team, it is very nice to contact with you here. This is Hui Shi from the IMS lab of the University of Tartu. We are making this pull request to propose a blob_detection_nodelet. The nodelet first implement thresholding, then morphological operations (optional, the users can turn it on or off in the launch file or using waikey under debug_view), the last is blob detection. We made some new features in the launch file, there is a new argument called debug_mode in line 8. It has four values : not_assigned, debug_view, ros, deploy. "not_assigned" as the default value will turn off this argument, in the case that the user want to just use the argument debug_view. "debug_view" for opencv view, "ros" for rviz and rqt_reconfigure view, "deploy" for running the node with configured params loading from a yaml file.

Looking forward to hearing from you . Thank you :)