Refactor autonomous subsystems

[tigressine]

The autonomous subsystem has some problems. I believe a cleanup/refactor will help me understand the subsystem better and also squash some bugs, namely:

• obstacle-detection node crashes at startup
• autonomous-control node doesn't die cleanly
• auto-drive crashes after orienting robot
• auto-home spins robot and then says it's home, no matter where it's actually positioned
• autonomous nodes are tied to Gazebo which prevents us from rolling out on real hardware or other sims

[tigressine]

A few of these issues are small fixes.

For overall refactor, should consider rosactions lib for autonomous routines.