Contacts: add further index modes (#420, #415).

You can search a Person by its entire name, either by phrase search or boolean search e.g.
{{{
    "Terry Winograd"
    Terry AND Winograd
}}}

You can search Persons and Institutions by combined Address terms, e.g.
{{{
    Hauptstraße AND Berlin
    10829 AND Berlin
}}}

For developers: you can key-search for a User Account topic by its username, e.g.
{{{
    curl localhost:8080/core/topic/by_value/dm4.accesscontrol.user_account/terryw
}}}
In preparation for #415 (Easify revelation of current User Account).

See ticket 420.
See ticket 415.