improvement for options handling of wb.ui.Base

We now make sure we overwrite the _options field, so instances will not share the prototype's
object!

As a visible effect, this fixes the language terms table's bug where all changes would be
saved to the last language in the list even though they were made for another language in the
table. This bug appeared because the options were shared between all Label/DescriptionEditTools,
this gets fixed by this change set.

Change-Id: Ibd4d327ccc69bfd75eb847f7528b73b4186b8fbb
Merge "improvement for options handling of wb.ui.Base"