Add CssImportFilter. More elegant fix for documents#348

Preview large TXT files fix

we also encrypt/decrypt files in the versions folder

we also encrypt/decrypt files in the versions folder for previews and if encryption is enabled/disabled

add /assets to gitignore

Bitmap class to handle all Imagick conversions to bitmap

Limit the size of the string generating the preview image for TXT files

Fix S3 copy and rename overwriting target directory

Redirect only to absolute URL

Use SVG previews for public sharing

Add flock to config

Fix PHPDoc

Remove invalid PHPDoc

This adds a file lock to the config in hope that this prevents race conditions as reported in https://github.com/owncloud/core/issues/11070

Testplan:

- [ ] Delete config.php and make it read-only => Error is thrown that it is not writeable
- [ ] Installation still works
- [ ] Changing config settings works (i.e. using the SMTP config switches in the administration menu)
- [ ] Your PC didn't blow up
- [ ] Installing the news app and the "Disable AppCode checker" app did not destroy your installation

Only skip the main config

Otherwise read only additional configs might not be processed

Test on tmpdir

Fixes https://github.com/owncloud/core/pull/11367#issuecomment-57306037 and https://github.com/owncloud/core/issues/9218

Despite the documentation this function does not read values from the cookie

Add clickable labels to encryption recovery radios

Close the session for preview generation

Add a CLI command that creates an empty LDAP config

[sharing] group shares

Remove dead code

We do not want to redirect to other domains using the "?redirect_url=" feature. Please notice, that the ownCloud project does not consider open redirectors as security issue.

dn needs to be fetched to be able to detect memberOf support

Without closing the session every preview image generation is locking the session which makes the webinterface unresponsive.

Try to create datadirectory to test whether the .htaccess works