Add a Calendar desktop plugin to lumina-desktop and lumina-config.
Remove the sample desktop plugin from being an option in lumina-config now that we have an "official" plugin.
Add a new desktop plugin: an application launcher.
This plugin allows the user to setup/launch a single application with a simple button press.
Also fix a couple bugs I noticed with the desktop plugin system:
1) Make sure container resize events get passed through to the main widget (so the visuals update properly)
2) Make sure the main desktop plugin area displays properly on multi-monitor setups. It needed to use parent coordinates instead of global coordinates.