estimate_joint should return similar output to estimate_R

[sangeetabhatia03]

For consistency, it would be nice if the R component in the output of estimate_joint could have a similar structure as the output from estimate_R.

[sangeetabhatia03]

As per our discussion today, we think it would be better to have an option (say show_daily_Rt, default value FALSE) so that we explicitly ask the user to specify if they want to view Rt estimates. Further, it might be better to return Rt in the same way as we are doing now to avoid comparisons with estimate_R. Would it not be better to rename the function estimate_epsilon rather than estimate_joint?