Rename RelatesTo for reply messages

Fixes Fluffychat messages containing null as the image dimensions
Fixes Facebookbridge not sending body, even though it is required, for
stickers
Fixes https://github.com/Nheko-Reborn/nheko/issues/166

No idea, if that is secure yet.

That's what the README suggests and - more importantly - the cmake
config file works with.
Also use angle brackets instead of quotation marks in two cases.