Add string::arg method in installTranslatorFunctions

QJSEngine::installTranslatorFunctions install the translator functions
to any given JS object. However, the custom string::arg() method is only
added in qqmlbuiltinfunctions.cpp, making the use of qsTr() in other
pure-JS programs quite hard.

Task-number: QTBUG-43113
Change-Id: Ia9ed97a4c07a4d167c792f3ea13e4f6e96c97423
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Update plugins.qmltypes

Change-Id: I9b6c54b572d4653d609b154000e274b9e64d591f
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@theqtcompany.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
qttest: make findChild available only for QtTest 1.1

Change-Id: I4ceb1a969bd4296b82f899088b02b5e8cf100bcd
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
QQmlInspectorService: handle views only with supported plugins.

Task-number: QTBUG-43048
Change-Id: I5b32bd0a1e28fdf56b5346580daf21e7ec1b9f8c
Reviewed-by: Kevin Funk <kevin.funk@kdab.com>
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>