Split up migrations to support dev/prod deployments

[thec00n]

Issue Type

[ ] bug report
[ x ] feature request

Current Behavior

Currently migrations are optimized for development deployments that are aimed to be fully automated and that have the maintainer and authority private keys available. For production deployments this will not be the case. Maintainer will be a multi sig wallet that authorize new extensions to the plasma contracts and the authority key will not be directly available to the child chain or deployment environment. Therefore the steps that require maintainer or authority signed actions need to be executed outside of the migrations flow.

Expected Behavior

Provide a boolean flag prod to the migrations script that is by default false and that skips actions that require the maintainer or authority keys.

[boolafish]

we do have the flag: DEPLOYMENT_ENV should be set to production though I guess it is not used by DevOps currently.