Code cleanup

See merge request !48

Additionally, removed unused empty constructor

Additionally, made first use of it in CouchDBDao.

Additionally, remove unused loggers.

Bump Java source and target versions to 1.8

See merge request !47

SessionServiceTest.testShouldDeleteAllSessionData fails when run on
JDK 8.

This will allow us to use type annotations, lambdas, etc. Documentation
already states Java 8+ as a requirement.

Robin Drangmeister authored 8 years ago and Daniel Gerhardt committed 8 years ago

This fixes WebSocket communication for course sessions. (dg)

Refs GH-40.

Changed `security.facebook.enabled-roles` to
`security.facebook.allowed-roles`.

Clean up code

See merge request !46

* Remove unused code
* Optimize imports (group 10+ and static imports)
* Remove redundant variable assignments
* Replace explicit type parameters with <>
* Remove redundant catch blocks
* Use varargs instead of explicit array instantiation
* Weaken visibility of methods and fields
* Simplify conditions
* Do not use StringBuilder for simple concatenations
* Fix code style
* Remove invalid Javadoc

Split up and rewrite  documentation

See merge request !44

Remove context.xml Servlet Container config

See merge request !45

The README file has been split up into separate files for installation
and development. A new documentation for the upgrade process has been
added.

The following changes have been made regarding content:
* Removed outdated Vagrant section
* Replaced unnecessary session persistance section
* Use simple HTTP proxy module instead of AJP for Apache httpd
* Nginx as alternative for Apache httpd
* Use Websocket proxy which makes HTTPS configuration on the Java side
  obsolete
* Additional configuration steps for server software
* Added requirements section
* Added upgrading instructions

The context.xml currently is only used to setup Tomcat's Manager
component. A file path for session persistence is set. This
configuration is unnecessary and complicatetes the setup since Tomcat
persists sessions by default without any additional configuration
according to
https://tomcat.apache.org/tomcat-6.0-doc/config/manager.html.