Dropped -provider icon and proper action text.

The formerly used icon is no longer provided by icon sets, so a switch
to an existing icon is needed.
See pim/kleopatra!16 (comment 428725)
and pim/kleopatra!16 (comment 428726)

Also capitalized action text.
See pim/kleopatra!16 (comment 428723)
and pim/kleopatra!16 (comment 428724)