Ensure Multi-plugin connection working

[atsushieno]

Currently AAP is not really stable if we instantiate two plugins on JUCE AudioPluginHost. For example, we can instantiate aap-sfizz (which so far only preloads a fixed sfz) and some effector from aap-guitarix (e.g. GxRat), connect from MIDI input to audio outputs, but after monkey testing onscreen MIDI keyboard AudioPluginHost crashes.

At this state we are not sure what's the source of unstability (JUCE AudioPluginHost on Android is very unlikely tested by the JUCE team because "there is no audio plugins").

aaphostsample so far instantiates only one plugin, so it's not usable for this verification.

A PoC plugin rack project would be useful.

[atsushieno]

As of current aap-juce and AudioPluginHost, we can connect multiple JUCE plugins (e.g. Hera and SimpleReverb), and it does not seem to crash, but the audio quality is disasterous. It can be improved by setting lower sampling rate (11.025 etc.) and smaller buffer size (e.g. 768 bytes), but there should be rooms for improvements.

[atsushieno]

Technically it is different from #40 (two plugins within a graph vs. just multiple apps) but in practice it can be unified into #40.