Additional refactoring needs to be done for the Run Selector plugin.

• Where possible, replace @DataBoundConstructor with @DataBoundSetter to minimize the Snippet Generator code output for Pipeline.
• Include the suggestions from the https://github.com/jenkinsci/run-selector-plugin/pull/1
• Find an appropriate name for the exposed API method. Current is pickBuildToCopyFrom(). A possible candidate may be selectRun()
• Any other changes that may seem appropriate.