Improve parse error when result is empty

[Sebastiaan127001]

Describe the bug
It would be useful if Quality-time gives more information when an API does not give the desired result.
For instance, if the user enters the wrong values in a source field, the API returns an empty list, but Quality-time still shows a parse error.

To Reproduce
Steps to reproduce the behaviour:

1. Go to a metric 'source up-to-dateness' with Dependency-Track as source
2. Enter 'latests' in the version field
3. Enter to refresh the measurement
4. See parse error

Expected behaviour
Two bits of information would better help the end-user.

• Show the full URL and path that has been used for this call.
• In this particular case, when an empty list is returned by the API, tell the user that an empty list was returned, instead of showing a parse error. Consider showing (part of) the data the Quality-time tried to parse so the user better understands why this did not work.

Screenshots