DummyEffect: removed inline specifiers, fixed header guard identifiers
EffectChain: remember original effect plugin data when loading dummy plugin

We don't want to loose the settings of an effect plugin even if it's not
available and thus can't be instantiated. Therefore remember original
settings data and save them back properly.

Partly closes #733.
initial work on LV2 support
LV2 support: plugins load and run; MIDI and GUI still broken
more work on LV2 support

Arbitrary plugins can now be loaded (no UI option for that yet).
LV2 support: refactoring
lv2: check if a plugin exists
lv2: fix noteoff issues by some mutex magic
typo
LV2: temporary UI for loading plugins
LV2: use SubPluginFeatures
LV2 features are now members of Lv2Base
initial LV2 state saving and loading. quite broken. may leak.
doesn't leak as much now.
lv2 features
more uri mapping