Move non-feather icons out of feather-icons directory

[jryans]

The feather-icons directory currently contains a mix of https://feathericons.com/ icons and ones from other places.

@ara4n says let's keep it to https://feathericons.com/ only, so we'll need a bit of detective work to sort them out.

[bwindels]

As we've forked feather-icons with the stroke thickness changes Nad did, I wonder how useful this will be, but meh :)

[jryans]

Fixed by matrix-org/matrix-react-sdk#2706