qmake: re-enable building of be.contacts

I wonder why this wasn't getting build in the first place -- perhaps some
screwup when splitting to use static libraries earlier when merging the abook
editor?
Merge branch 'qmake-fix-be.contacts'

REVIEW: 110976
Cleanup: make the code clearer

Signed-off-by: Jan Kundrát <jkt@flaska.net>
Imap: toString(const FlagOperation op) implemented to eliminate code duplication

Signed-off-by: Jan Kundrát <jkt@flaska.net>
Make it possible to mark mailboxes as read in a single operation

fixes #606
REVIEW: 110742

Signed-off-by: Jan Kundrát <jkt@flaska.net>
Merge branch 'mark-folder-read'