Minor fixes of styling, add codehilite, change datalink modal

[kimakan]

This PR adds following changes:

• minor changes in styling, e.g., styling of the table in the metadata of a schema
• a number of minor fixes, like fix of an mysql adapter ( it fixed also the ci tests) or rendering of the filepath in the results table
• added codehilite for the rendering of the code in the markdown files
• Major overhaul of the datalink modal. I simplified it quiet a bit for the user. We will provide links only for the previews (if exist), downloadable files (if exist) and all image previes with the semantic #preview-image or #preview-plot. If the user wants something else then there will be a link that leads to the full datalink viewer.
  So...now it looks something like this

[coveralls]

Pull Request Test Coverage Report for Build 12984621735

Details

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall first build on style-minor-fixes at 64.428%

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Totals
Change from base Build 12884297015:	64.4%
Covered Lines:	4994
Relevant Lines:	7189

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💛 - Coveralls

[jochenklar]

Thanks! I have some minor suggestions regarding JS syntactic sugar and I guess styling is always a bit about taste.