Add support for deployments to multiple accounts and regions

[whimzyLive]

Overview

Currently pipeline bootstrapped by doostrapper is only capable of deploying to same region and in a same account. This is not very useful for many projects. doostrapper should be able to create pipeline that can perform cross-region and cross-account deployments.

Idea

It needs to behave something like this,
i) Tools account contains all deployment resources, (i.e dootstrapper resources)
ii) Dev account is more like a sandbox where all merged code gets deployed as part of build process to verify that last commit was a success
iii) Test accounts contains almost stable (releases)
iv) Prod account

read more here

Checklist

• configure stacksets to trigger deployments to multiple accounts

blocked by #56

[whimzyLive]

Cloudformation stacksets are not yet implemented in cdk aws/aws-cdk-rfcs#66, so if stacksets needs to be used, cdk apps must be transformed to cloudformation stacks first.