add support for single-instance launching of applications

[Bill Filler]

Would be a nice enhancement to have the ability to change the default behavior of the launcher to launch only one instance of a given application. If the application is running and it is clicked again from the launcher, the running instance should be brought to the foreground. The current behavior is to launch a new instance of the application each time it's clicked from the launcher.

[Neil J. Patel (njpatel)]

    * Add support for single instancing of applications so, once the user has
      launched an application from the launcher, clicking on the application icon
        again will bring that window to focus (if it still exists).

    * This behaviour is default, but can be changed back to the old style by
      setting /apps/netbook-launcher/disable_single_instance to true.

    * We probably need to have middle-click cause a new instance regardless of
      single instancing (like a new calculator instance). Also maybe a entry
      in the right-click menu too?

[Neil J. Patel (njpatel)]

Added middle click support for launching a new instance of a application that's already running (even if it isn't, middle-click will launch an instance).

Not going to add to menu as we can't always be sure that an application has a window associated with it (requires going through all the windows every time), and the wording would be weird..."Launch new instance", "Launch another instance", "Launcher second instance"?

Windows opened outside of the launcher aren't dealt with currently as it's a bit tricky to get that right. However, going to file a bug about it and attempt to fix it next week.

[Neil J. Patel (njpatel)]

External windows bug: https://bugs.edge.launchpad.net/ubuntu/+source/netbook-launcher/+bug/328581

[Paul Larson (pwlars)]

This bug has been moved to Ubuntu distribution