Improve uninstaller

[shannah]

Right now jDeploy registers an uninstaller on Windows, but it still depends on the jDeploy installer application to do the uninstalling. It would be better if the launcher knew how to uninstall directly without needing the JVM. In addition, we should add full uninstall support on Linux and Mac. We have begun to write manifests of the files that are added, along with CLI command support. We should add support in the launcher to be able to read these manifests and delete the files that were added. No UI necessary.

[shannah]

I added detection in the installer to see if it is already installed. If installed, instead of an Install button, it shows an Update and Uninstall button.

When you click the Update button it does the same as Install. Uninstall will uninstall the app.

[shannah]

Uninstall via Installer app added here 89f2733

This doesn't address the headless uninstaller.