plugins: DegreeToKey - avoid duplicate struct entries


Signed-off-by: Tim Blechmann <tim@klingt.org>
lang: headers - declare public functions only once

Signed-off-by: Tim Blechmann <tim@klingt.org>
scapp: schedStop() on application terminate

fix for assertion failure on scapp quit.
fixes #726

Signed-off-by: Tim Blechmann <tim@klingt.org>