LocalInstallHandler should not work on the critical path

LocalInstallHandler.install() is called on the main plugin/webstart thread before we finish preparation of resources and launch the application.

However, as part of the installation process it might be creating images and this may cause delays. As well as OS interaction.

This should not block main thread. In fact this is example of the task that can be done AFTER application is launched in the background thread. Some other tasks are also nice to move out from the critical path, e.g. creation of tray icon, etc.