feat: "Keep Together" (avoid page break) feature

[batonac]

I believe it would be a fairly simple feature and immensely helpful to be able to apply a "keep together" rule to elements to ensure that they are never spread between pages.

Here's an example of the issue I'm referring to:

And here's the desired outcome (div is kept to together and pushed to the next page):

I believe this should be as simple as applying the css rule page-break-inside: avoid; (for wkhtmltopdf) or break-inside: avoid; (for a more modern renderer) to the object in question. The easiest way to improve our print formats would be to automatically apply this rule to the rectangle elements, but the more sophisticated way would be to add a toggle for a "Keep Together" attribute on individual elements.