Bugfix: Fix json escaping

[MDK5]

Motivation, Context and Description

Fixes #73.

The problem is caused by insuffiecient escaping. Gson correctly escapes the quotes inside the string as \", but for reasons I do not understand, the artemis connector receives all quotes as \", both inside the string and the ones part of the json. Therefore it cannot distinguish them anymore and the parsing crashes, leading to the described bug. To counter this, all backslashes get replaced by double backslashes before sending the data to the connector.

Also comments breaking changes regarding the testRun flag that would otherwise cause syncronisation issue with Orion's and Artemis's releases.

Steps for Testing

1. Install the release as described in the readme
2. Test with the latest develop
3. Assess an exercise
4. Add all sorts of special characters into the feedback
5. Verify the feedback gets stored correctly on the server, e.g. by opening the same submission in the browser

[lschlesinger]

I tested it with providing feedback including several backslashes and other non-character signs. The feedback shown in Artemis showed the feedback string without any changes. Solution works well to fix the issue 👍

[willergeorg]

Code changes lgtm.

[Malyuk-A]

Tested during testing session. Used locale Orion version. Code was explained and seems to work fine.