Added a few functions to derive keys from passwords. Currently it
supports PBKDF1 and PBKDF2 as defined in
RFC 8018 ( https://tools.ietf.org/html/rfc8018 ).
[ChangeLog][QtNetwork][QPasswordDigestor] Added QPasswordDigestor
Task-number: QTBUG-30550
Change-Id: I2166b518bd8b54e3486514166e76fd9ba2f219c8
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>