* Remove Raspberry pi Docker file
* Remove old show-source/solution and plan button
* Remove commented out code
* Improve navigation
* Remove underline from navigation and remove margin of left navigation button
* Make arrow a bit smaller so it aligns a bit better with the navigation bar itself
* Remove Guava dependency from WebGoat
* Add Checkstyle to the project with very basic standards so we have a
style across lessons. It does not interfere with basic Intellij formatting
- Now using Spring Boot for classloading, this way local development does not need to restart the complete server
- Fixed all kinds of dependencies on the names of the lessons necessary to keep in mind during the creation of a lesson.
- Simplied loading of resources, by adding resource mappings in MvcConfig.
- Refactored plugin loading, now only one class is left for loading the lessons.
