Add event bundle selection to "Add a reaction rule" form

In D7 we had the ability to restrict entity events to a specific bundle type when configuring a Reaction Rule.

When you did "Add a reaction rule" in D7 you got an Ajax-enabled form. The form asked you to choose the rule name, machine id, tags, and description. Below that it asked you to select an event to react on. When the event was selected, if it was an entity event, then an additional selection was made available via Ajax to let you restrict the event to a specific bundle.

For example, if I chose: "After saving a new content item" (rules_entity_insert:node) I would then see a selection element allowing me to specify the bundle, or content type, of the event. For example if I only wanted to react on new "Article" nodes being added, I could turn this event into a qualified event: "After saving a new content item of type Article" (rules_entity_insert:node--article). Then, our reaction rule would only execute if an Article was created, and would not fire if any other content type was created.

This patch accomplishes all of the above for D8. It works completely, but there are still a few things I'd like to change before committing:

I'm not very happy with the way the event labels were modified in RulesEventManager. I also still need to port the test to WebDriver (I initially copied some of the test from known-good JavascriptTestBase code, so I wanted to ensure the patch works in the testbot before I started porting the test to WebDriver). I would also like to enhance the FunctionalJavascript test and add some Functional tests.

Please test and review this patch and let me know if I missed something.

EDIT: JavaScript test now ported to WebDriver.