Split up and rewrite documentation
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- Removed outdated Vagrant section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