some cleanups
Xwt.DroidBackend.DroidExtensions: rename Default => DefaultSettings
Xwt.DroidBackend.DroidContextBackendHandler: bug in Arc
Xwt.DroidBackend.DroidContextBackendHandler: DrawText needs prepend of matrix values
Xwt.DroidBackend/DroidDesktopBackend: do not normalize ScaleFactor with 160/96
Xwt.DroidBackend.TextWrapper:adjist baseline and lineHeight
Xwt.DroidBackend.DroidExtensions:Matrix.prepend, FontFactor, FontSize, Context conversion