Add a green test for the eventCounter projection for each language

[rradczewski]

If implemented, this would help people get started with working on the projections themselves instead of fiddling around with the initial setup.

Needs to be done for every language, but can be done one after another

• c++
• clojure
• csharp
• elixir
• elm
• fsharp
• java
• js
• kotlin
• php
• python
• ruby

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Possible aspects of a green test

• The test works on a sequence of all event types so deserialization of all event types is tested as well (that has been an issue at the DDDBER workshop)
• The .travis.yml has been adapted so the green test runs on Travis as well
• The test is already a bit overdesigned & -refactored (e.g. Event-factories and utilities that help with time-dependent projections

[tcoopman]

Can we start with a PR in one language to discuss it? I would propose that the test is easy and obvious.