including install space node, timeout for initial pose, and covariance defaults / configurable

[SteveMacenski]

Adding node install space for people that use the install space rather than devel space for deploying.

[SteveMacenski]

I also added a timeout for the number of attempts parameterized in the launch file to get the initial pose before just using a relative measurement in response to my own desire and #8

[SteveMacenski]

finally, adding in reasonable covariance defaults in the message

[lianshangni0922]

I think it should be changed like this ：
initial_robot_pose.pose.pose.position.x = 0; initial_robot_pose.pose.pose.position.y = 0; initial_robot_pose.pose.pose.position.z = 0; initial_robot_pose.pose.pose.orientation.w = 0; initial_robot_pose.pose.pose.orientation.x = 0; initial_robot_pose.pose.pose.orientation.y = 0; initial_robot_pose.pose.pose.orientation.z = 1;

[SteveMacenski]

That's true, but this PR has been dead for while anyhow. Not sure anyone is going to merge it but it implements the covariance variables