Doc: Update external links to point to doc.qt.io

Task-number: QTBUG-43062
Change-Id: Ic630f0c7af20ab5ffa88a71a6ab99d42250cf272
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>
Doc: new template for qt.io online style

An online documentation template that follows the
style of qt.io site.

Update the url variable for Qt modules to point
to doc.qt.io/qt-5/.

Task-number: QTBUG-42086
Change-Id: I5428a02cd503aef2217efd7361f4c8b7b5895a52
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>
Android: Fix broken system palette

When we overwrite the default palette, we have to make sure
we don't overwrite default values with black for all the
colors that are not retrieved from the json file. We would
for instance get black as both the base color and text
color which would make some components unusable.

Change-Id: I1079a70a0ac7eb379ed5e8d92c6b39c2ea77ba49
Task-number: QTBUG-42812
Task-number: QTBUG-42998
Reviewed-by: BogDan Vatra <bogdan@kde.org>
Reviewed-by: J-P Nurmi <jpnurmi@theqtcompany.com>