Refactors SC.MenuPane to use SC.ListView internally

[nicolasbadia]

SC.MenuPane no use SC.ListView internally in order to be able to display huge lists of items.

• Events are now dispatched to the list view.
• SC.MenuItemView now extend SC.ListItemView and uses SC.Control instead of SC.ContentDisplay.
• Selection is now managed with SC.SelectionSupport.
• This commit also add a new actOnSubMenu property, and allows separators to have a title.
• SC.MenuSeachPane height is also now correctly computed, which solve an issue when only one item is displayed.
• It removes support for itemExampleViewKey as it is complicated to implement with SC.ListView and doesn't really make sense.
• It also removes localization support as this is not supported by SC.ListView.
• I also included a CSS cleanup and removed SC.ContentDisplay as it is not used anymore

[mauritslamers]

I disagree with removing SC.ContentDisplay. It might not be used here, but it is very useful to have in many other circumstances.

[nicolasbadia]

I reverted the SC.ContentDisplay removal and added support for itemUnreadCountKey.
I also fixed an issue with SC.Record and added a test for it.

[nicolasbadia]

I updated the last commit with the suggested adjustements.

[mauritslamers]

A few things:

The commit 7f7e730 turns out to be responsible for the failing tests (https://travis-ci.org/sproutcore/sproutcore/builds/350716397#L1740), as a change in the title of an item in the items is no longer picked up as there is no mechanism for it.

Also I think the commit history is a bit messy, as it removes and then re-adds functionality. It also includes changes to for example the designer framework, which is more or less dead weight IIRC.
I would therefore suggest that we break this PR up in a few separate ones and also squash a few commits in order to get a more logical commit history.

There seems to be a contradiction in the description up, specifically where you mention that you remove the localization support but in the resulting code the localize setting on the view is still there. Is the change that you removed the option to automatically localize all the menu items?