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

Hi,

I'm not sure wether this was the intention behind the cucumber.eclipse.runner plugin, but the wiki page suggested so (in my reading) and the plugin had no code so far. Let me know if you'd rather prefer something like a cucumber.eclipse.launching plugin.

As the commit indicates the main intent here is to decouple the editor further from the dependency on Cucumber-JVM and the JDT. That way making it possible to use the editor for editing feature files but running them through a completely different gherkin-execution-framework.