Update README file
Update README file

- Add Gitter badge with link to chatroom
- Bump copyright date
- Update requirements to 1.3.0
- Move Compatibility section below Installation, convert to table and
  add links to download zip files
- Reference Compatibility section in the setup instructions
- Revised and reworded Support section, add reference to Gitter chatroom

mantisbt-plugins/source-integration,make-all/source-integration,make-all/source-integration,make-all/source-integration,dregad/source-integration,dregad/source-integration,mantisbt-plugins/source-integration,dregad/source-integration,mantisbt-plugins/source-integration