Add dynamic handling of ROS master

[mathemaphysics]

Currently, when rosrun lidarshooter LiDARShooterGUI is run (or if invoked directly) the interface may hang until roscore is running on localhost. We should still be able to start up the main GUI without the master server running. There should be a panel or even for the time being just button indicating that the master can't be found on localhost (or whichever default server it points to).

This will be the first step to enabling dynamic connectivity to the ROS master server. We'll eventually want a tab or settings panel which can be used to select the host and port of the master to connect to.

Our initial acceptance criteria will be modest.

Acceptance Criteria:

1. rosrun lidarshooter LiDARShooterGUI should start up the GUI with no hang
2. On startup, LiDARShooterGUI should display some indicator that the ROS master is present and connected or not
3. For the time being, assume that the master will always run on localhost; it will either be running or not

More stories will expand on this.