[#1059] Added support for SVG logos

[Bartvaderkin]

Note I had to update some dependencies to get SVG support in django-filer

[Bartvaderkin]

@jiromaykin I'm not 100% sure if the CSS changes are OK, as you explicitly added those height:auto; 's, but it doesn't work if I keep them.

Note I also needed to set a height-attribute on the SVG's image element for it to show up, but then that would break the non-blurry-images for regular pixel images so I made it adaptive.

I got some SVG's from here: https://www.cityofenschede.com/en/brand (particularly the wide logo)

[jiromaykin]

[...]'m not 100% sure if the CSS changes are OK, as you explicitly added those height:auto; 's, but it doesn't work if I keep them.

OK @Bartvaderkin - i needed those heights for mobile, in order to not prevent the images stretch/shrink really weirdly - but i will check to see what happens with SVG's and other images. And... maybe different thing happens if the user uploads SVG's that have an inline style?

[jiromaykin]

This seems completely fine actually - I've done some really weird testing with strange SVG's and the only SVG's that do not behave well are the ones with inline-styling and without an explicit viewbox - so: if users upload correct and valid SVG's then the styling behaves well (something to note for ourselves in case future users report problems with SVG).

[Bartvaderkin]

Ugh yes invalid or weird SVG's are a complication. The SVG used should at least look normal in a browser/viewer without margins (viewbox and transforms etc)