[new compiler] Fix scope, binding target and property object for bindings in group properties

Resolve the confusion about _qobject and _qobjectForBindings, use _qobject for
all property related bits and _qobjectForBindings is gone, in favor of
_scopeObject. Usually they are the same, but in group properties for example,
the _scopeObject remains the outter object but the _qobject becomes the
object that's returned by the group property, i.e.

   anchors.fill: parent

For that binding, the scope object is the outter object but the _qobject
is the value of the anchors property.

Then there's binding target, which is revelant for value type properties, where
it remains the outter object. In theory one could nest a value type property in
a regular group object, in which case _scopeObject would be outter most,
_qobject would be the value type wrapper and _bindingTarget would be the group
object.

Change-Id: Ie3135d951910bf40ece192ab6260d7a9e6e9cdd6
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
[new compiler] Fix error handling for property names that look like signals

The check for the right hand side of a potential signal handler declaration
needs be placed after we determined that we are really assigning to a
signal.

Change-Id: I7f5417dc30ba7365327560e1b16ee9ceaa9bed76
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
[new compiler] Fix mix of bindings and signal handlers

When storing a binding, we remove any previous binding. If we store
a signal handler, we look up the same property, but we must not destroy
any existing bindings:

    property int someThing: { ...}
    onSomeThingChanged: { ...}

Change-Id: Ie5afd986ee3d8b4f2efd0aabca331c33a225abfc
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
[new compiler] Fix assignments to enums from string literal

This is the quick fix for the tests. Later we'll need a pass that resolves
this and changes the QV4::CompiledData::Binding::Type according to the
resolved value of the property.

Change-Id: I5a799873ae8fb7f716a6af22f7e67927820c2513
Reviewed-by: Lars Knoll <lars.knoll@digia.com>