Implement sent message history (up/down keys).
Implement sent message history (up/down keys).

This includes preserving and restoring partially entered text per room. This
is mostly ported straight from Angular.

vector-im/vector-web,KentShikama/vector-web,vector-im/vector-web,vector-im/riot-web,vector-im/riot-web,vector-im/riot-web,howethomas/vector-web,neko259/vector-web,vector-im/riot-web,pvagner/vector-web,davidar/vector-web,KentShikama/vector-web,Bitcoinsulting/vector-web,KentShikama/vector-web,vector-im/vector-web,vector-im/riot-web,KentShikama/vector-web,KentShikama/vector-web,vector-im/vector-web,vector-im/riot-web,martindale/vector,pvagner/vector-web,martindale/vector,KentShikama/vector-web,vector-im/vector-web,neko259/vector-web