Setup App Server with REST API + Database Server + Continuous deployment via branch

[bennyboer]

BLOCKED: Need to wait for server (VM)

We need a REST API in order to use firebase cloud notifications and target specific user groups.
Thus setup the server (VM) with a Java application server + database server.
Develop application which realizes the REST API.
Lastly setup continuous deployment of the REST API application to the application server via a GitHub branch which builds the application on Travis and deploys it to the application server.

(Optionally) Use Let's Encrypt to encrypt http connection of the server to the app.

[thomai]

(Optionally) Use Let's Encrypt to encrypt http connection of the server to the app.

The REST API will use the same certificate than the other FS websites. However, this is not a problem since HTTPS is used by-default.