Allow payment modules to change postsale parameters "mod" and "id" (#1137)
Fixed comparison of module id
Needle/haystack order of strpos()

According to [documentation](php.net/strpos) the parameters have to appear the other way around, else the call will always return false.
Merge pull request #1168 from systemhaus/feature/payone-postsale-fix

Needle/haystack order of strpos()
Merge branch 'feature/payone-postsale-fix' into hotfix/2.1.4