Marc edit, pop up suggestion box when editing 6XX fields

[Pasi Kallinen]

When editing the 6XX fields, and entering any text, the editor should pop up a suggestion box. The user can then either pick one of the suggested entries, or enter the (new) text. Entering new characters updates the contents of the suggestion box.

The contents of the suggestion box come from the database, from the same field and subfield, ordered, in descending order, by the number of times that text appears in that field.