Print loading no visual feedback

[filleg]

Describe the bug
When printing a PDF you get no feedback that work is being done in the background. Using a higher DPI or other settings that are demanding it can be mistaken for that something has gone wrong and the user tries to reload the page etc.

To Reproduce
Steps to reproduce the behavior:

1. Print a A3 PDF in 300 DPI

Expected behavior
Some kind of spinner maybe, open for suggestions.

Additional context
The possibility to abort a print would also be nice, without having to reload the page.

[Grammostola]

Visually: The blue progress bar from the main map and control "progressbar"? It is a known quantity for showing the progress of tiles of a map loading. Since the print preview map is always visible currently then the mentioned progressbar would always be also and seems fitting (the two buttons would re-enable when the progress was complete). If so then logically: it isn't currently wired to be reused wherever and would need adapting to be more generalized in terms of which map and where to be drawn.

An alternative could be a spinner next to the two buttons when they are disabled. Would provide (additional besides the buttons) visual feedback but not progress. There is a spinner in utils/. (The other, large spinner that happened when either print button was activated now seems to only manifest from the Save image print button)