Add widget to build a multi-transaction from its composing transactions

[Gaudeval]

Users are currently expected to type in their multi-transaction (in the transactions view) for filtering. It would be more interesting to use an auto-complete field to quickly fill a set of transactions. This was prototyped with some success in the symmetry notebook.

• The widget would provide a multi-transaction name, or a list of transactions, as its model.
• The widget would allow a user to select all each transaction from the whole set in the model, a subset matching the current multi-transaction, or a subset matching additional filters.
• The widget would allow a user to copy or edit the name of the multi-transaction would be an appreciated.
• The widget should be reusable between views or notebooks (might need more documentation on how to nest ipyvuetify widgets)