Rewrite the accessibility intro/overview docs
Rewrite the accessibility intro/overview docs

Change-Id: I9b821ea9318b02a7c6c0756ee72163c5becb1d3f
Reviewed-by: Jerome Pasion <c10995d24f6b454503389e8d00d837aef038985d@digia.com>

kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc