Include pledger's declared state in MailChimp integration

[furf]

When a user subscribes to MailChimp, include their declared state code (i.e. CA, WA, DC).

The merge field key is |STATE|.

[furf]

Notes:

It's possible that all that has to be done here is to send the state field in with the right MERGE## as the field name

This: https://github.com/Lessig2016/pledgeservice/blob/master/backend/handlers.py#L534

But it only works in /r/subscribe

Change needs to be made here: https://github.com/Lessig2016/pledgeservice/blob/master/backend/handlers.py#L216

And then the parameter added and passed through here: https://github.com/Lessig2016/pledgeservice/blob/master/backend/handlers.py#L445

Mailchimp has 2 keys for every paramenter a default key which is MERGE## and then a custom key which, in this case, is "STATE"

there are two lists in there: one main one and one test one

the custom (MERGE) fields should be the same in both lists, but check that

pledge-test pushes into the test list

live system into the live list