Fix python-quietclean Makefile target.
Add bindings/swig/classes.i to Python binding dependencies.
Java: ignore Meta::get_config() due to SWIG typemap issues.
Java: Move interfaces into org.sigrok.core.interfaces, tidy build system.
Java: correct input map type in create_output() wrapper.
Add config key for amplitude.

This is intended for setting (or getting) the amplitude of a source
which doesn't really have an MQ associated with it, such as the demo
driver's analog channels.
demo: Support changing the amplitude of analog channels.
output: Rename instance private storage pointer to priv.

This makes it consistent with other libsigrok fields used for this purpose.
demo: Attach analog generator to channel, not channel group.

This also adds a new channel group "Analog", which has all analog
channels in it.
output/wav: Initial module skeleton.
output/wav: Initial module implementation.