fix #1033 Removing wrong lines in the MultiAutoComplete.

This commit removes two lines which set a new value in
the data model when pressing tab if the field is empty
and not positioned at the end of the options (i.e. when
leaving the edit mode through tab if the field is empty).

There is no reason to set the value at that time as the
value has not changed, and this can lead to the onchange
handler being called later when the value has not changed.
fix #1038 Updating skin property for MultiAutoComplete widget

This commit updates the multiautocomplete property for skins.
fix #1032 viewport sizes updated when the first autoresizable element is registered
viewport sizes are now also updated when the first autoresizable element is registered, and not only when Layout singleton is loaded or a resize is done.