Improve System Shutdown Speed

[zthorson]

Description

Some threads were slow to shut down, taking 5-10 seconds after system shutdown to fully exit. This appeared to be primarily caused by the FPS timers not being interruptable, but there were other minor shutdown tasks that would take a while.

Reason

A quicker shutdown allows us to release resources quicker on systems, allowing a full restarts of the code in a shorter time frame.

Method / Design

Changes included:

• Change the OpenRealm::Timer code to use conditional variables in the wait statement allowing the timer to be interrupted
• Moved the shutdown code for pose estimation to the finishCallback to start shutting down vslam earlier in the shutdown phase
• Set the OpenVSlam terminate flag to help exit their loop quicker

Testing

Compiled and run on: Ubuntu 20.04 - Desktop

Other Notes

[laxnpander]

Looks good, seems to be running. Merged!