ToolBox bindings for declarative containments

This adds the necessary bits, actions handling, showing / hiding of
toolbox and a hooks for config interface and add widgets.

The interesting bits:

Toolbox separate on the scene

For declarative containments, we add a declarativewidget on top of the
view which loads the "org.kde.toolbox" package. The toolbox can differ
per platform, layout of toolbox and containment can not "leak" into each
other.

ToolBox import

The most important and interesting bit is the list of actions the
ToolBox exposes, it's collected from corona, containment. The latter is
actually problematic, since we don't get access to the actions
internally provided by Containment
(ContainmentPrivate::addDefaultActions).
Containment::setToolBox(AbstractToolBox) being protected, we cannot
register our declarative ToolBoxProxy implementation to the containment,
so we have to wire up settings and addwidgets separately. Sorting of the
actions is "random", and expected to be done by the QML toolbox
implementation, based on objectName strings.

REVIEW:107232