message: Filled empty Changelog.md and added changes
diff: +# Changelog
  +All notable changes to this project will be documented in this file.
  +
  +The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
  +and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
  +
  +## [NEXT]
  +### Fixed
  +- Fixed wasteful course data usage #654 via specialized course model interfaces.
  +- Fixed a broken documentation link #583.
  +- Limited the first- and lastname to 64 characters in registration- and edit page. [#585](https://github.com/h-da/geli/issues/585)
  +- add correct E-Mail validator to edit-profile and register component [#564]
  +- Upload of profile pictures now prevents files with wrong extensions [#581] (https://github.com/h-da/geli/issues/581)
  +
  +### Security
  +- Fixed multiple severe course related security issues #594, #653.
  +
  +
  +## [0.6.0] - 2018-03-31 - Introduces MediaManager and some minor changes
  +### Added
  +- MediaManager for file management in courses
  +
  +
  +## [0.5.0] - 2018-03-24 - WS 17/18 intermediate Release
  +### Added
  +- selective download of the course
  +- progress dashboard for teacher
  +- translateable frontend with i18n
  +- notification system added
  +- introduces new error message system
  +- dark theme option
  +- introducing an api documentation
  +- courses are ordered by last visit
  +- user password edit
  +- adds imprint
  +
  +
  +## [0.4.0] - 2017-12-04 - WS 17/18 Second feature release
  +### Added
  +- Responsivness improved
  +- leave course function
  +- delete course
  +- import/export course function
  +- free text mail to students
  +- dragging content between lectures
  +- consistent save and abort btns in units
  +- progress component
  +- duplication of lectures
  +- randomize tasks after validation
  +
  +
  +## [0.3.1] - 2017-11-05 - Dynamic db name update
  +### Added
  +- The possibility to use a other database name then 'test'
  +
  +
  +## [0.3.0] - 2017-11-02
  +### Added
  +- a lot of major bugfixes and optimizations
  +
  +
  +## [0.2.2] - 2017-10-19 - Security improvements
  +### Added
  +- security for free courses
  +
  +
  +## [0.2.1] - 2017-10-03 - First Live-Ready release
  +### Added
  +- first live functionality
  +
  +
  +## [0.2.0] - 2017-06-29 - Almost production ready
  +### Added
  +- Many new feature for production
  +
  +
  +## [0.1.0] - 2017-05-11 - Basics implemented
  +### Added
  +- Many basic implementations of ground functionality
  