Add TextDocument::messageHighlighted(msg) [signal]
Revise TrayPlugin
Refactor SoundPlugin
Rename SoundPlugin to AlertPlugin
Refactor DockPlugin
Add WindowPlugin
WIP: refactor TrayPlugin to use WindowPlugin
Add PluginLoader::pluginInstances()
Make MainWindow responsible for WindowPlugins
DockPlugin: make use of WindowPlugin
init/cleanupBuffer => add/removeBuffer
init/cleanupConnection => add/removeConnection
init/cleanupDocument => add/removeDocument
init/cleanupView => viewAdded/Removed
init/cleanupWindow => windowCreated/Destroyed
Restore ImporterPlugin