improvements to the examples

[goatzillax]

I'm just dropping a number of improvements that would improve the experience of these examples. I have some of these in my local tree but maybe an expert should take a crack at it.

1. Add a headless mode. Disable overlays, dump everything to fakesink, and obviously disable all syncing.
2. Change detection.py to use tiling. As far as I can tell, the detection example is basically tiling with 1 tile. So it's a subset of a tiled example. Given how unreadable and difficult these pipelines are to construct, I think this would be a much more demonstrative and helpful example.
3. Either fix the hangs or build in a watchdog. In file mode the code hangs quite a lot -- I can't imagine how you guys are managing to get through a release process and regression with this many hangs. A very brief look at utilization shows it's hanging at or near the end of a run while polling for some file descriptor. Maybe put a sensible timeout in the poll, or pop up a watchdog thread. Or fix the hang. Pick one, two, or all three, but don't pick none.

[giladnah]

@goatzillax can you please share which RPi 5 you got (4GB / 8GB) and which video encoding and resolution you use?
In addition please make sure you enabled the PCIe gen 3.