Update install guide for current versions for dependencies

• Update CouchDB section for version 2
• Remove "or newer" for OpenJDK (ARSnova 2 does not run on JDK 11)
• Adjustments for Debian 9/10
• Install Tomcat 9

src/site/markdown/installation.md

@@ -72,7 +72,7 @@ you can follow CouchDB's guides to set up CouchDB 2:
 * [Single Node Setup](https://docs.couchdb.org/en/stable/setup/single-node.html)
 
 After CouchDB is installed successfully, [set up an admin user](https://docs.couchdb.org/en/stable/config/auth.html)
-with the credentions set before for `couchdb.username` and `couchdb.password`.
+with the credentials set before for `couchdb.username` and `couchdb.password`.
 
 We provide a Python script that will set up a new database for ARSnova.
 This "Setup Tool" is located at [thm-projects/arsnova-setuptool](https://github.com/thm-projects/arsnova-setuptool).