Endpoint for editing rate laws

[cthoyt]

Yohann asked for the following:

In the HMI, they want to edit a rate law, but when they do this, they aren't easily able to keep track of any new parameters that might get introduced. For example, they might introduce an N parameter for total population to normalize the rates. They want this to automatically get added to the parameters list. They don't necessarily give an initial value, this would get added in the HMI in a subsequent step.

We should code up a new endpoint that does this and keeps track of adding new parameters nicely.

Input:

1. An AMR
2. The name of the transition
3. The new rate law for the transition

Desired output:

1. A new AMR with the rate law replaced and any new parameters added