We reintroduce the possibility to mount the app in first position in
a target. The option "self" has been dropped since it is now possible
for a component to have several top level nodes.
We re-add the possibility to validate props when dev mode is active.
No change in the API right Now. The dev mode is activated via the
configure method of App class.
This commit brings back the possibility to translate text nodes and
the attributes "label", "title", "placeholder", and "alt" in an app
configured with a suitable translation function.
It is also possible to deactivate translations under a node via
the directive t-translation="off".
For flexibility it is possible to define the list of translatable
attributes in the app.