Add option to allow html in column names

[puehringer]

#480 introduced text sanitization, which makes perfect sense in the default case (especially for values coming from APIs).

Sometimes however one would explicitly want to do that while ensuring it is safe, which includes setting "static" column names, descriptions, ... For example, adding a little info-icon to the column name showing some tooltip is currently not possible:

User story

We want to show additional HTML in the column headers (and only the headers, not values, etc. for now). The relevant lines were introduced here: https://github.com/lineupjs/lineupjs/pull/480/files#diff-405214671f4c41381345a91ca70d7dd417bbec1bbcb6db6cdd2406e3268114eaR35-R43
Would it be possible to add an unsafeLabel or htmlLabel property/flag to the column description to explicitly allow HTML (default should remain safe)?

[sgratzl]

what if the user is editing the label? would it then be safe or unsafe?

[puehringer]

Good point, I would expect the user to simply see the HTML-string, i.e. when I mark a column as unsafe I am also responsible for disabling the rename (if I want that). If a user adds renames an unsafe column to something containing HTML, it should "execute" that I suppose. That's just my very first idea, I am open to suggestions.

I also noticed that currently something is wrong (possibly because of the ") in https://deploy-preview-480--lineupjs.netlify.app/injection.html: