Introducing plugins manager

res/test_plugin/plugin/__init__.py

src/sakia/app.py

src/sakia/data/entities/__init__.py

src/sakia/data/entities/plugin.py

src/sakia/data/files/__init__.py

src/sakia/data/files/plugins.py

src/sakia/gui/dialogs/plugins_manager/__init__.py

src/sakia/gui/dialogs/plugins_manager/controller.py

src/sakia/gui/dialogs/plugins_manager/model.py

src/sakia/gui/dialogs/plugins_manager/plugins_manager.ui

src/sakia/gui/dialogs/plugins_manager/table_model.py

src/sakia/gui/dialogs/plugins_manager/view.py

src/sakia/gui/main_window/controller.py

src/sakia/gui/main_window/model.py

src/sakia/gui/main_window/toolbar/controller.py

src/sakia/gui/main_window/toolbar/view.py