Allow network encoders (and other hot-plugged tuners) to be detected after startup.

Currently, capture devices are only looked for during MMC's init, so if sage starts up faster than a network encoder, sage might not see the device. This is fine for already detected encoders that are in the sage.properties and configured, as those will be retried, but if it's a new encoder that has not been configured, it will not. There is a MMC.redetectCaptureDevices that was added at some time, but there is no API link to it. I'm looking for input on potential issues of adding an API function for this, and calling it when entering the source configuration screen in the STV.