Move launching code that depends on JDT/Cucumber-JVM to a separate plugin

Create a new plugin for this code as it depends on JDT/Cucumber-JVM to
do the launching. These dependencies tie the editor to a particlar cucumber
implementation which is undesirable for re-use of the editor component.

Minor oddity: Using a cross-plugin reference for the icon did not work out
when launching the plugin into an Eclipse 3 build. Possibly not supported
by the corresponding UI that shows the launch configuration. So the
cukes.gif image is copied from the cucumber.eclipse.editor plugin.
Remove the runner plugin

It served no purpose so far and the launching code for cucumber-jvm is in
a different plugin. Lets just remove this dead stuff.