Validate json for importing and exporting TTL data

[SarahRemus]

Related issue

towards #932

Context / Background

We are currently developing the functionality of syncing the TTL data to Google Drive, related to #913.

When importing the data, it would be good to validate if the given JSON file is in the correct TTL format. As discussed in #932 this functionality can also be useful in other parts of the project.

What change is being introduced by this PR?

I implemented the functionality to check whether a JSON file is in the correct TTL format. For that I oriented my self on the code in import-export.js as some form of a validation is also done there, however it's more intertwined with the rest of the code and not easily reusable.
There are some functions in time-math.js I could have used, but I decided to reimplement them as they have the following flaws (in my opinion, maybe I'm overlooking something):

• the isValidDayOfMonth(dayOfMonth, month) function can't handle leap years
• I'm pretty sure the regex used in validateDate(date) is only going to November and not December
• (1|2)[0-9]{3}-(0[1-9]{1}|1 [0-1] {1})-(0[0-9]{1}|1[0-9]{1}|2[0-9]{1}|3[0-1]{1})

How will this be tested?

I wrote a bunch of unit tests, testing all kinds of different data input. But we definitely have to do more tests once the functionality is integrated with the sync-data-to-google-drive functionality.

[thamara]

Hi @SarahRemus, thanks for your patience with this (and others) PR.

I really liked the idea of the json scheme validator, but was under the impression we needed to sort out the whole google drive thing first.
But looking at it now, I believe this PR can already be included, and we should seek a further work to replace our hand-made json validator when importing a database with this cleaner solution.

Please let me know if you'd like to still work on this PR, otherwise, I can include the suggest changes and merge it.

[thamara]

Actually, the changes were very minor, so I was able to quickly address them and will merge this shortly.

[thamara]

\changelog-update
Message: Enhancement [#946]: Included formal json scheme validator
User: SarahRemus

[thamara]

This was merged, but because it was merged directly into main, GH is not able to identify it. So closing it.
Thanks @SarahRemus!