flow dev should start flow emulator

[chasefleming]

Currently, to use flow dev you have to start the emulator and then also start flow dev. Considering this is supposed to be a way to simplify development, it would be nice to reduce complexity. The only potential issue I can see is with state. Although, I don't think that people using flow dev are generally considered with starting from a new state each time given the way accounts are created. @bluesign any thoughts?

[chasefleming]

Note: we'll need to use a flag to not break current usage. In 2.0, we could do it automatically if we wanted.