<rdar://problem/4359736> Support outlining ability with lists

        Added Mail SPI for list level changes.  It is SPI because it is not complete support
        for outlining.  See <rdar://problem/4457070> "API for html lists as note outlines".
        
        * WebView/WebHTMLView.m:
        (-[WebHTMLView _canIncreaseSelectionListLevel]):
        (-[WebHTMLView _canDecreaseSelectionListLevel]):
        (-[WebHTMLView _increaseSelectionListLevel]):
        (-[WebHTMLView _decreaseSelectionListLevel]):
        * WebView/WebHTMLViewPrivate.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@13080 268f45cc-cd09-0410-ab3c-d52691b4dbfc