QmlDesigner: Make getters const in ViewManager

Change-Id: I30dd4775b9e23d540a451ef7086cc623473be03b
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
QmlDesigner: Make DesignDocument::view const

Change-Id: I0d1b8fb55fbd08d556b0daa2d4a7d12bc81c4c13
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
QmlDesigner: Share contextHelpId

Moved the code to AbstractView::contextHelpId so it can be shared.

Change-Id: I0a95b5ee079cbc26c87d53587f7766f1c333a245
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>