Support per-monitor input source configuration.

[AaronFriel]

The configuration is extended with a monitor_input_map property and JSON and TOML format support.

This allowed me to do this:

usb_device = "05e3:0610"
monitor_input = "DisplayPort1"

[monitor_input_map]
1 = "DisplayPort1"
2 = "Hdmi1

[haimgel]

Thanks for the PR! I took a bit different approach... wanted to have a symbolic map as I move my laptop quite a bit between locations and "monitor #1" is not specific enough, I wanted to match on brand/model/serial number.