Introduce FlickablePage and ListViewPage components

[Tim Peeters]

FlickablePage and ListViewPage are intended to be used instead of the current Page with a Flickable or ListView as Page.flickable. Having a FlickablePage/ListViewPage will be less confusing for the developer, and it makes things easier to implement (with less hacks/workarounds in detecting and updating the Page.flickable item).

Currently in Page we try to detect a Flickable or ListView and depending on its anchors and settings we change its topMargin to take our application header into account.

Introducing FlickablePage and ListViewPage makes it easier to set default properties of the Flickable and ListView, and allows us to control which of the Flickable/ListView parameters the app developers can override. We can use it, for example, to define an optimal horizontalVelocity of the Flickable depending on the number of grid units on the device.

[Tim Peeters (tpeeters)]

Having the Flickable as an internal property of the FlickablePage would allow us to easily control scrolling speed, as is needed to fix this bug https://bugs.launchpad.net/ubuntu-ui-toolkit/+bug/1348557