Android: Support double click event

It's impossible to get the distance between two touch events
down to 5 pixels on e.g. my Nexus 5.

This patch makes it possible to tweak the distance through
the platform theme, and sets the distance to 15% of an inch
on Android. Also provides a way to override the default minimum
of 5 pixels by using an environment variable.

[ChangeLog][Android] Fixed double click events

Task-number: QTBUG-36974
Change-Id: I23d94020c531747d6638b645133611614a2a0703
Reviewed-by: BogDan Vatra <bogdan@kde.org>
Use QStringIterator instead of homebrew

Task-number: QTBUG-15664

Change-Id: I1ed3eb04ddd822e57a4d993af656dfe283f3af1a
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Avoid using direct OpenGL calls in gui and widgets

Change-Id: I5d88a2e204ca23e178a4e3044b9cb13392c3e763
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>
Doc: correction link, example and parameter issues qtbase

Moved codecs folder to qtbase/examples
Corrected quote in dropsite.qdoc
Replaced snippet statement by include statement
Added doc for undocumented parameters

Task-number: QTBUG-34749

Change-Id: If4de95b8d39e5680fd0f63f8d2b6685a4b0a8052
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
Revert some previously added constexpr in QVector?d classes

This commit partly reverts cd91d8ad0281c984a01b8091696a6fdfdfa69514.

The revert is required as the used ifdef relied on undefined
compiler behavior. Especially Windows has had trouble. The revert reduces
the risk of breaks by future compilers.

The proper inline and constexpr has to wait until Qt 6.

Task-number: QTBUG-37122
Change-Id: I881fffb95fa46d9c170c9420a578f15640e18aea
Reviewed-by: Lars Knoll <lars.knoll@digia.com>