TableViewStyle: Add header delegate for Android style

The whole TableView concept doesn't map very nicely on Android
(and in mobile in general). However, for completeness, we provide
a fully implemented TableViewStyle.

For the header delegate, we re-used the design for section headers
which is close enough, specially since it's not uncommon to see
sticky section headers in mobile applications.

This change depends on another change in qtbase, which takes care
of extracting the 'listSeparatorTextViewStyle' element.

Change-Id: I9c50e4c7cabdc6b0ea864cef3da55ae3d7337d79
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
SwitchStyle: Make it work with pre-Holo Android

The Switch control was introduced in Android 4.0 together with
the Holo UI. Therefore, there's no way we can extract assets
on devices running earlier versions. In that case, we fall back
to the Base style Switch visuals.

Change-Id: I48d8a5cd94999cd5687fab62c8d16beb4fc53b5c
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>