feat: filtering folders in mailbox picker

[madbob]

General review of the MailboxPicker component, including:

• removed custom breadcrumb, and using NcBreadcrumbs
• removed most of the custom CSS style
• added a filtering text box (as required by Search input for the mailbox picker #11158 )
• fixed a reference to a missing variable, introduced in 084cc67, causing errors in the JS console when the "Move Thread" action is selected

#11158 is not entirely fixed as it is still missing a "Recent selected folders" option, which in my opinion can be interesting and for which I require some feedback.
Introducing a new server-kept preference seems to be an overkill, a disposable client-side array where to save the (latest 5?) selected folders would be recommended. But I've not been able to find something like a "client-side only store", some place where to keep informations just for the current session. A new src/store/localStore.js, where to keep some arrays, may be an acceptable solution?

Edit: fixes #7536 (similar to #11158, not including the Recent/Favorites part).

[madbob]

Note to myself: the "disposable localStore" will be useful also for #616