Add warning to README
Add MTI ROS constructor for online mode.

This constructor initializes the frequency from mti messages
Add camera ROS constructor for online mode

It reads camera info to get camera parameters and image messages
to get the frequency
Inform camera init time to camera hardware on main.hpp
Load parameters and frequencies from topics when working online
Save used parameters on file after initialization

Some parameters may be over written when running online. Now we save
the files so we have the correct parameters for a replay.