Added new SignToolHelper
Implemented old SignHelper method

Added the old method provided by the old SignHelper and marked it as obsolete. Renamed the properties "File" and "Password" of the SignCert type to "CertFile" and "PasswordFile" to make it more clear what they mean. Also added documentation to those properties.
Merge pull request #535 from Bomret/feature/signtoolhelper

Added new SignToolHelper