Route for thumbnail generation

Thumbnail generation

Removed Log

Added requested changes

Added requested changes.

- Fix code style
- Add exception if file does not exist
- Switch route styling

Replaces https://github.com/owncloud/core/pull/10805

Fix codestyle

Fix codestyle

Migrate to appframework

Fix typo
Merge pull request #11009 from owncloud/tobiasKaminsky-route

REST API for thumbnails