Fix InterpolatorServer.connect.

The axis number was not taken into consideration when creating the synth.
Also ReplaceOut seems safer than Out in that context.  A safety was added to
make sure connecting to an axis that do not exist is impossible.
Add getters to help debugging.

Also makes refresh rate faster.  This is the version that was used for the eBuzz 2013-2 performace (2013-05-03).