Update to module version v1.5

- fundamental revision of backend configuration
- improved multistore support
- support of one-page-checkout added
// Updated CONTRIBUTORS.md
Merge branch 'master' of github.com:SOFORTPM/PrestaShop-modules into SOFORTPM-master
Sofort : Config files removed & version updated in config.xml
Merge branch 'SOFORTPM-master'
// Updated CONTRIBUTORS.md
Boxdrop : New module added
Merge branch 'master' of https://github.com/PrestaShop/PrestaShop-modules