Pedalpi-pluginsmanager

**********************************
- Fix ``pluginsmanager.util.builder``: Add folder in pip

**********************************
- Add class method :meth:`.Lv2EffectBuilder.plugins_json_file`

**********************************
- Add lilvlib support:
- Add object Lv2EffectBuilder method - :meth:`.Lv2EffectBuilder.lv2_plugins_data`: Scan and generate the lv2 plugins metadata
- Add object Lv2EffectBuilder attribute - :meth:`.Lv2EffectBuilder.plugins`: List plugins
- Add object Lv2EffectBuilder method - :meth:`.Lv2EffectBuilder.reload`: Load lv2 metadata

**********************************
- Refactor :class:`.util.persistence_decoder.PersistenceDecoder`: Using now design pattern;
- Fix :class:`.ModHost`: Bug when changing value of a parameter from a plugin;
- observable_list: Add method :meth:`.ObservableList.pop`.

**********************************
- Initial release