Multi device support

[Enzo-Kerkhof]

Dear Christian,

I'm testing the Magewell dual DVI device with your repository for a research implementation.
As far as I now understand in your current release it is not possible to easily switch between devices or input channels.
I've tried to run your example script, which works fine for input 0. For input 1 though it cannot read the time from the device after changing the 0 to a 1 on line 266 of pro_capture_device.py in the function capturer.mw_get_device_path(0, t_path).
It then throws an exception in: _get_device_time_in_ticks line 197.
Though it does not break anymore due to no video signal detected.

Would there be an easy implementation of making it possible to start 2 capture instances to grab frames with the same timestamp?

Best,
Enzo