Little green men to indicate 1:1 rooms in the LeftPanel

[ara4n]

This is the cosmetic feature issue to complement #2070, spun off from #1884.

This is tracking actually putting the little green men badges on 1:1 rooms in the LeftPanel, once #2070 is done.

[ara4n]

This is now unblocked by matrix-org/matrix-react-sdk#446