backend and frontend: show pdt-vallex links to lexemes
In the NomVallex data, some values of the attribute
pdt-vallex are links to full lexemes rather than individual lexical units (the string after the attribute name is not an id of a lexical unit, but the prefix common to all lexical units of the given lexeme/lemma), e.g.
Right now, the string is parsed as an id of an LU which is not found in the database.
We need to find a way of parsing the string as a lexeme id (but right now, there is no concept of lexeme ids!) and then showing the full lexeme in the pop-up after clicking the attribute value.