[WIP] Remove loadAppScriptFile

:warning: This is WIP do not merge

This removes `loadAppScriptFile` and enforces the usage of proper routing.

Fixes https://github.com/owncloud/core/issues/9060

# Todo

- [ ] core
- [ ] files
- [ ] files_encryption
- [ ] files_sharing
- [ ] files_trashbin
- [ ] files_versions
- [ ] user_ldap
- [ ] user_webdavauth
- [ ] Send mail to developer ML