Revert E-puck name to e-puck

[ygoumaz]

#574 fixed the name from e-puck to epuck in the rats life example.

To be consistent with the default name of the E-puck, this PR reverts the change and modifies the name from epuck to e-puck in the launcher and the epuck_world instead.

[omichel]

Did you test that the service names published by ROS are working fine with the dash in the robot name?

[ad-daniel]

In theory names are sanitized here:

webots_ros2/webots_ros2_driver/src/Driver.cpp

Lines 39 to 41 in db38ed5

	std::string robotName(wb_robot_get_name());
	for (char notAllowedChar : " -.)(")
	std::replace(robotName.begin(), robotName.end(), notAllowedChar, '_');

[ygoumaz]

Yes I tested and it works fine. Dashes are replaced by underscores.