Add unit tests

[dagwieers]

While I initially thought unit testing would be easy, I now have to conclude it is not that simple 🙄

[dagwieers]

Basic encoding unit tests have been added in #93

[im85288]

@dagwieers The Travis build is failing with an issue with Python 3.5. This is what I could see in the logs

`
Traceback (most recent call last):
File "/home/travis/build/im85288/service.upnext/test/test_encoding.py", line 71, in test_to_addon_signals
decoded_data = AddonSignals._decodeData('["%s"]' % encoded_data) # pylint: disable=protected-access
File "/home/travis/virtualenv/python3.5.6/lib/python3.5/site-packages/AddonSignals.py", line 21, in _decodeData
return json.loads(base64.b64decode(data[0]))
File "/opt/python/3.5.6/lib/python3.5/json/init.py", line 312, in loads
s.class.name))
TypeError: the JSON object must be str, not 'bytes

`

Hopefully you have access to the Travis results? https://travis-ci.org/im85288/service.upnext/builds/617623308?utm_medium=notification&utm_source=email

[dagwieers]

Our unit tests are failing for a genuine bug in Addon Signals: ruuk/script.module.addon.signals#6

We are also waiting for ruuk/script.module.addon.signals#4 to be merged so we can use the upstream master branch, rather than my branch.