Generic can extension

This proposal exists because Ini-config files are deprecated. In this proposal there is not importat which middle-ware is used since the configuration parameters are given in constructor. In my case is used inside ROS, but think is better when doesn't depend on any ROS-specific code (like ROS-parameters).

Tested and used is only PCAN-USB dongle, I don't have possibiliy to test for other CAN interfaces, so empty functions are in other CAN implementations.

Also some constants are added to CanItf.h file to make configuring easier.

*Note:* It would be good to discuss this changes, because than this can be used as a standard-way for slowly transition form Ini-config fils to ROS-Parameter-files. Other possibility is that Can implementations depend on ROS-Parameters explicitly (as now depends on Ini-files), which I don't prefer, because even the ROS is kind a standard in robotics today this code can be used outside ROS, which can have advantages for embedded systems.