Document usage of JavaSript functions in .ui.qml files

We need to document which JavaScript functions are supported in QDS 1.1.

Its most functions from

http://doc.qt.io/qt-5/qtqml-javascript-functionlist.html

And the translations functions.

List of supported functions in .ui.qml files:

"qsTr", "qsTrId", "qsTranslate",
"qsTrNoOp", "qsTrIdNoOp", "qsTranslateNoOp"

"toString", "toFixed", "toExponential", "toPrecision", "isFinite", "isNaN", "valueOf", "toLowerCase", "toLocaleString"
"toLocaleLowerCase", "toUpperCase", "toLocaleUpperCase", "substring" , "charAt", "charCodeAt", "concat", "endsWith", "includes", "indexOf", "lastIndexOf"_

Functions from the 'Qt' scope (http://doc.qt.io/qt-5/qml-qtqml-qt.html):

_"lighter", "darker", "rgba", "tint", "hsla", "hslv"
"point", "rect", "size", "vector2d", "vector3d", "vector4d", "quaternion" "matrix4x4", "formatDate", "formatDateTime", "formatTime"_

Additional all functions of the 'Math' and 'Date' object are supported.

This should be documented in http://doc.qt.io/qtcreator/creator-quick-ui-forms.html.