ActionSelectionPopover doesn't scroll when there are too many items to display

[Michael Sheldon]

Steps to reproduce

 1) Run the following QML on a phone:

import QtQuick 2.0
import Ubuntu.Components 1.1
import Ubuntu.Components.Popups 1.0
import Ubuntu.Components.ListItems 1.0 as ListItems

MainView {

    useDeprecatedToolbar: false

    Component.onCompleted: {
        PopupUtils.open(menuPopover);
    }

    Component {
        id: menuPopover
        ActionSelectionPopover {
            id: menuList

            actions: ActionList {
                Action {

                    text: "Test 2"
                }
                Action {
                    text: "Test 3"
                }
                Action {
                    text: "Test 4"
                }
                Action {
                    text: "Test 5"
                }
                Action {
                    text: "Test 6"
                }
                Action {
                    text: "Test 7"
                }
                Action {
                    text: "Test 8"
                }
                Action {
                    text: "Test 9"
                }
                Action {
                    text: "Test 10"
                }
                Action {
                    text: "Test 11"
                }
                Action {
                    text: "Test 12"
                }
            }

            delegate: ListItems.Standard {
                text: action.text
            }
        }
    }

Expected result:

 Should be able to reach all items in the list

Actual result:

 List overflows the edge of the screen and doesn't scroll, so "Test 12" can't be reached.

[Cris Dywan (kalikiana)]

This affects the header, which now subclasses ActionSelectionPopover internally for its OverflowPanel, and becomes unusable if there is more items than fit the window height.