Prepare changelog for v0.12.4
Prepare changelog for v0.12.4

vector-im/vector-web,vector-im/riot-web,vector-im/riot-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web,vector-im/riot-web,vector-im/riot-web,vector-im/vector-web,vector-im/vector-web,martindale/vector,vector-im/vector-web,martindale/vector