Autorunner functionality
This commit enables the automatic launching of multiple auto-run programs when monado-service is started. It is designed to be able to be expanded upon in the future with options on how to launch each autorun program, and I plan to add some of the functionality before this commit is merged.
In addition to all the things I marked with @todo, some current limitations:
- CMake configuration is not quite complete and likely sub-optimal. I have recently gotten it working, but I am not sure if it will work in every situation.
- Due to being unsure how a program can be launched and then tracked on Windows, this commit does not currently support Windows. I may add another commit to do basic launching without tracking in the future, though (by using os_threads instead of pthreads).
- Android functionality is also not currently enabled.