apps like files_versions still get the old signature version

use the version of the original file if we write the part file to have a proper version if we move the file over to the original location

Saves a call to fetch the file id which didn't even work for a reason.

This fix properly sets the version in the database.

don't decrease ->version for part files but only a local variable, otherwise it can happen that we decrease it twice and end up with the wrong value

realPath should contain the path to the file we want to read, e.g. the version and not the original file

Prevents switching single blocks within the encrypted file.

This way it is not possible anymore for an external storage admin to put up old versions of the file.

The previous IV was actually 12 byte extended to 16 byte using base64. As the encrypted file should be fine with containing binary data as well we can simply remove the encoding like that here.

CTR is recommended over CFB mode.

Makes static code analyzers happier.

1. Variable is not defined
2. Method does not expect any parameters

```
Undefined variable: user at /Users/lukasreschke/Documents/Programming/master/apps/encryption/settings/settings-admin.php#45
```