[FIXED JENKINS-19173] API to mark an Action to hide from context menu

[JENKINS-19173](https://issues.jenkins-ci.org/browse/JENKINS-19173) Added `Action.ContextMenuVisibility` annotation and a method to `Functions` to determine if the annotation is present (if it is not, then the `Action` will be visible) and check if the `Action` is marked as not visible. Updated `actions.jelly` to use this method and set the `contextMenu` attribute. Also, added a test to test the annotation.