CMake finds correct Eigen config in Ubuntu 14.04.

The installation tutorial instructs to install Eigen3.  A standard
Ubuntu installation has no FindEigen.cmake, but only FindEigen3.cmake.
Therefore, I instructed CMake to require Eigen3 instead of Eigen.
Compatibility update for ROS Indigo.

CvBridge does not have the imgmsg_to_cv function anymore, but it is
renamed to imgmsg_to_cv2.
kalibr_bagcreater can now handle short filenames.

Previously, filenames had to be at least 10 character, without filetype
extension.  When a filename was shorter, an empty string would be passed
to int(), which results in a ValueError.  With this version, when an
empty string is encountered, secs is set to 0.