SVG preview generation should work for callouts and maps

[farley13]

For callouts - we likely just need to inject some css that reduces the font size as is currently done when we generate svg previews for tables or axis labels.

For maps - This is likely going to be a good deal trickier. One issue is that the SVG used for maps in leaflet is actually almost 2x larger than the visible portion of it - I think likely to reduce issues with scrolling. In addition to the size, it has a pretty drastic view transform applied to it. In testing I found we can capture the svg to show, but trying to get it to fit into a given area is harder. As an example - if you remove the width=100% and height=100% from the svg inline partial view - you'll see we do have the full svg available - but it will be shown overlapping other previews because it's so much smaller.

[akarasev]

GUI of the articles has been changed since I've seen that last time. First of all, I'm unable to choose dataset for a visual layer. The list is empty, however I've loaded sample dataset. My bad, works fine actually. Also, could you provide some sort of mock-up for the task? I think, it might be a simple screenshot with some marks.

[farley13]

This is what the map screen looks like on an actual article:

to see the preview on the homepage, delete the styling for the image -

It now should show up with the right shape/color but much larger than we would like:

For the callout - when we look at it in the article view - it's relatively small:

but in the preview - the stroke width is much too large and the text does not show up:

[farley13]

@akarasev Callouts look much better - we will push the map portion as per email