Rename files, refactor filtered_input into input_filter.

All '-' become '_' in filenames.
`filtered_input` has become `input_filter` and all functions are
prepended with this.
Add input filter banks.

Allow multiple instances of input_filters in an application.

TODO: Apply this to filters, sdp_tx and ensemble.
For ensemble this is useful for global inhibition, for filters and
sdp_tx it allows more than one Node/Ensemble to feed to component.