Unify akka versions used by dependencies

**Branch, version, commit**
`develop`

**Actual (wrong) behavior**

There is a lot of evictions in dependency resolution also the following warning, when starting the application:

```
[2020-08-27 19:25:56,107] WARN akka.util.ManifestInfo [ManifestInfo(akka://akka-test)] - Detected possible incompatible versions on the classpath. Please note that a given Akka version MUST be the same across all modules of Akka that you are using, e.g. if you use [2.5.30] all other modules that are released together MUST be of the same version. Make sure you're using a compatible set of libraries. Possibly conflicting versions [2.5.22, 2.5.30] in libraries [akka-multi-node-testkit:2.5.22, akka-persistence:2.5.22, akka-protobuf:2.5.30, akka-coordination:2.5.22, akka-actor:2.5.30, akka-slf4j:2.5.22, akka-remote:2.5.30, akka-cluster:2.5.30, akka-stream:2.5.30, akka-cluster-tools:2.5.22]

```

Dependency on `2.5.30` was introduced by `"org.sisioh"%% "akka-cluster-custom-downing`.

No specific file or test is named. Start by locating the dependency declarations and the org.sisioh akka-cluster-custom-downing dependency, then inspect dependency resolution for the Akka modules listed in the warning. Done means all Akka modules resolve to one compatible version and the evictions and incompatible-version warning no longer appear.

Written by the indexing model from the issue text.