Fix p7m and p7s file extensions for Windows 7

Authored by aheinecke on Jul 18 2018, 3:21 PM.

Description

Fix p7m and p7s file extensions for Windows 7

* src/inst-kleopatra.nsi, src/uninst-kleopatra.nsi: Register
for P7MFile and P7SFile.

On windows 7 those two are used instead of .p7m and .p7s