Add modulation-based filtering ability.

[darksidelemm]

Adding modulation filtering ability would be handy, and allow filtering to specific payload 'types' (e.g. WSPR floaters).

Unsure where the best place for this is in the UI. We already have similar to this in SondeHub-Professional with the radiosonde type filtering, where the type is put into the search box (e.g. 'RS41'). We could do similar?