Support multiple networks

[onbjerg]

It would be cool to support multiple networks such as Rinkeby where Aragon is deployed.

A simple implementation of this might be as follows:

• We run a worker for each network we want to support, each with an environment variable ETH_NETWORK set to their corresponding network name.
• Every top-level document (such as entries in the orgs and apps collections) have a property network attached to them
• The API should be able to filter on these top-level documents using a network name
• The website should have a simple dropdown with the supported networks

I estimate that if the feature is implemented like this we would be looking at around 4-5 hours of work with the caveat that infrastructure costs will scale linearly with the number of networks we support, since we have to run a worker for each network. Furthermore, if we want to eventually run archive nodes, then we'd have to run one for each network too.

Networks we should support:

• Mainnet
• Rinkeby
• Flora