* introduce exchange info selector support
Adds support in selectors/exchange for queries based on
backup.ExchangeInfo entries. This allows the declaration
of selectors based on non-identifier details such as sender,
subject, or receivedAt time.
Changes Exclude scope matching from being an Any-
match comparator to an All-match. This keeps exclude
and include behavior identical, hopefully making less
confusion for users.
* move config unions to common code
The configuration union handlers in Storage and Account
overlapped significantly in behavior. Moving those helpers into
a common code folder was requested. Although the behavior
was similar across the files, the types were not, requiring
the addition of generics to solve the need.
