Feature/show qos incompatibility

[trittsv]

This Pull-Request adds the possibility to display basic qos incompatibilities between readers and writers on a topic.

The gui looks like this:

The yellow warning triangles besides the domain and topic indicates the user that there is a mismatch. Besides that in the topic view readers and writes with yellow rectangles show which are affected. When the user hovers over a reader or writer then the specific incompatibility is shown in the tool-tip text.

What it currently cant do is qos xtypes check, this will be implemented in a separate pull request. To try to keep the pull requests relatively small.

@eboasson can you have a look into this pull request?

[trittsv]

@eboasson thank you for your review. I did some modifications - may you can check again?

• i moved the qos code from dds_service.py to dds_qos.py - which then later can find its way into the python-wrapper
• i changed the check_qos from only return one mismatch to return a list with all mismatches (the qos objects are already present in the gui, so only the policy id is needed).
• the entity_type will be changed to Endpoint with two subclasses in a other PR (with some other changes i want to make in the data handling)