Implement message previews as outlined in #443
Implement message previews as outlined in #443

wakermahmud/cryptocat,Raynes/cryptocat,wakermahmud/cryptocat,DGO143/cryptocat,DoNotUseThisCodeJUSTFORKS/cryptocat,PeterDaveHello/cryptocat,arno01/cryptocat,PeterDaveHello/cryptocat,DoNotUseThisCodeJUSTFORKS/cryptocat,DoNotUseThisCodeJUSTFORKS/cryptocat,Cryptodog/cryptocat,Cryptodog/cryptocat,DGO143/cryptocat,Raynes/cryptocat,Raynes/cryptocat,arno01/cryptocat,DGO143/cryptocat