Fix: drop ids from namespace

With the new liquidsoap versions all sources have a unique id, this id is used to create the namespace for the corresponding telnet commands. Since we alter the sources in liquidsoap multiple times we have a miss match in the namespace of some telnet commands. `mixer.inputs` returns a list of sources which may contain a id. This id is concatenated with the name of the source. For example `in_stream_0.1` is a valid response from `mixer.inputs`.  We therefore drop everything after the first `.`.