Rebase communitheme on GNOME Shell 3.27.92 and switch to bionic

[didrocks]

OSK classes have been impacted. Use the upstream colors when applicable
for now and use upstream svg.

[didrocks]

Note: CI will now stall as tzdata is waiting for an answer:

debconf: falling back to frontend: Readline
Configuring tzdata
------------------
Please select the geographic area in which you live. Subsequent configuration
questions will narrow this down by presenting a list of cities, representing
the time zones in which they are located.
  1. Africa      4. Australia  7. Atlantic  10. Pacific  13. Etc
  2. America     5. Arctic     8. Europe    11. SystemV
  3. Antarctica  6. Asia       9. Indian    12. US
Geographic area: 

We should ignore it for now. I'll have a look to force debconf no-ui next week.

[didrocks]

I would need your review @clobrano on that one as well, please :)

[clobrano]

Hi @didrocks, sorry, I was sure to have merged it already. LGTM 👍