Add support for Android 9-patch images in BorderImage

The 9-patch image implementation in Qt Quick Controls 1 is an internal implementation detail of the Android style. It cannot handle .9.png image files out of the box, but takes a normal image without borders and the border information separately (as it was provided by the Ministro style assets).

• http://code.qt.io/cgit/qt/qtquickcontrols.git/tree/src/controls/Styles/Android/qquickandroid9patch_p.h
• http://code.qt.io/cgit/qt/qtquickcontrols.git/tree/src/controls/Styles/Android/qquickandroid9patch.cpp

The existing implementation could serve as a fine starting point for implementing a proper generic QQuickNinePatchImage. It just needs to read/strip the border information from the image file instead of providing such QVariantLists for the borders in the API.