[BUG] clipboard api pasting brings html markup instead of json string only

[marabesi]

Describe the bug
Whenever copying the json from another browser or even from code editor (that has some style embedded) the pasted json shows html markup that shouldn't appear.

To Reproduce
Steps to reproduce the behaviour:

1. Go to any web browser that formats json (that is not the json-tool)
2. write some json to be formatted
3. copy it with the keyboard shortcut
4. Go to the json-tool
5. click on the button to paste json from clipboard

Expected behaviour
See the json string formatted without additional text

Current behaviour
Currently the tool shows a markup that is not part of the json, probably it is something to keep the format from the place where it was copied