Make icons consistent

[nadonomy]

Icon spacing is all broken in the top right, and uses distinctly adhoc icons (e.g. travis's pin icon for pinned messages; rick's modular icon; luke's share icon)... all of which need to be homogenized

[nadonomy]

Closing for this sprint, although we'll continue to iterate on this in future.

[jryans]

Fixed by matrix-org/matrix-react-sdk#2370.