Remove side effects from code caused by `init()`

[joschahenningsen]

Our code utilizes the init() function go automatically runs at package initialization. Most people recommend avoiding this https://github.com/uber-go/guide/blob/master/style.md#avoid-init as it makes the code unclear and less testable. For instance: The worker could try communicate with TUM-Live when tests are run because it's initialized using init().

Avoid depending on the ordering or side-effects of other init() functions. While init() ordering is well-known, code can change, and thus relationships between init() functions can make code brittle and error-prone.

This is an issue as well in our dao packages. When the daos are initialized the DB variable might not be set yet, causing calls to somedao.db to fail.