Provide option to anonymize node

[chris-smith]

• Adds support for anonymous option when calling initNode to anonymize your node name. Follows rospy logic.
• Fixes error message when unable to find message package.
• Also some unintended whitespace changes? Maybe from Atom?

e.g.

rospy.initNode('/my_node', {anonymous: true})
.then((nh) => {
   console.log( nh.getNodeName() ); // "/my_node_25878_1464120320242"
});

[IanTheEngineer]

Isn't this FIXME still true? String validation of the node name hasn't changed.

[chris-smith]

I meant to remove it when I added the validation that exists. There is, admittedly, a lot more name validation/mapping that we need to do, though this exists for most ROS names and not specifically for node names.

[IanTheEngineer]

Looks great overall. I'm ready to merge as is.