Allow uploading files

[kghbln]

This is only possible with $wgGroupPermissions['*']['upload'] = true; set in LocalSettings.php which should rather be avoided. So allowing new people to upload e.g. a profile photo or some resumee or CV only during the registration process will indeed be a nice feature.

[kghbln]

Uploading malicious files should not be possible or is deliberately allowed: #20 (comment)