Add sponsor logos

[Kriesse]

On /sponsors/:
Add SinnerSchrader logo ( file from last year).

@hblank Any other logos that can be added now?

@silkine Any ideas about layout?

TODO:

• Adjust the spreadsheet-import script to fetch sponsors (Add sponsors page #152)
• Adjust styling for the /sponsors/ page (Add styling for sponsors #161)
• Add a CTA to "become a sponsor" to the /sponsors/ page
• Re-do the copy shown on the /sponsors/ page
• Add sponsors to the footer

[Kriesse]

Design by @silkine is here:

Sponsors Page:

Design for footer on all other pages:

[silkine]

Here lives the svg background, can be implemented exactly like the speaker svg background, tiled vertically:
form-sponsors.svg
https://drive.google.com/open?id=1C63zZ4A4__jTwFCwN0IU-VfcGfq01vcQ

[silkine]

also the responsive layout of the sponsor page can be pulled out of the footer layout. I saved a "grid" view, that might be helpful: