Refined Directory Structure and added functionalties

[vinay0410]

Hi @codebot ,

• Shift Redundant code to training placeholder directory
• Added launch file for cv_camera ( usb cam doesn't work on MacOS )
• Vision msgs can now be installed from debian packages sudo apt install ros-<distro>vision-msgs. Therefore, changed readme for that.
• Option to select different model by changing params in the launch file. This would prevent users from altering the code, and if this package is released then it would be better to change launch file rather than code.
• Model will be only downloaded if user doesn't provide model path, Earlier it was being downloaded anyways while running cmake.
• Better Error and info logging

Update:

• Also fixes Wrong Centroid calculus #2 , i.e. fixed centroid calculation in L145-L146

Thanks!
Any feedback on the same would be very helpful.