[JENKINS-13995] Disabled the automatic pop-up of context menu.

Instead, it shows a small 'v' icon to the right that needs to be clicked
to open a context menu.
Fixed the wrong border that appears below the first context menu item.
Jenkins!
documentation
GMaven needs to use the same provider as the Groovy core uses.

This is based on
http://stackoverflow.com/questions/13113142/gmaven-build-fails-with-an-api-incompatibility-was-encountered