Add display control DDC/CI modules

[ttimasdf]

This PR added backend implementation for manipulating monitor configurations as part of timmo001/system-bridge#3344, more specifically,

1. brightness
2. contrast
3. audio speaker volume
4. power state
5. input source

getting and setting SDR Content Brightness on HDR monitors is also planned, since brightness control is ineffective when HDR is enabled. But it may require further discussion since implementation may involves a C++ extension and direct manipulation through ctypes is a bit tricky.

[ttimasdf]

This commit 8b6ddb7 is a big one since it touches various modules to add a communication channel between threads.

Also, it corrects the behavior of UpdateThread and DataUpdate. Currently DataUpdate.request_update_data will create new, duplicate DataUpdateThread every time because self.update_data_thread.is_alive() returns False since DataUpdateThread forks into a (unnecessary, anonymous) child thread and exits immediately.

So, DataUpdateThread is modified to not fork into new threads and added parameters for partial data update.