Rename ReactPerf to Perf
Rename ReactPerf to Perf

As this makes it work out of the box with react-perf chrome
extension (which doesn't do a whole lot other than save you having
to remember the commands, but is still quite nice).

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