Nicaea export state

[mnaamani]

Exporting state from nicaea, members, forum state and versioned store to be imported at genesis in a new chain.
There will be a corresponding set of PRs to monorepo that imports json produced from these scripts:

To test, run a nicaea local node:

yarn
node lib/export_members > members.json
node lib/export_forum > forum.json
node lib/export_versioned_store > content.json

The path to each output file can be used as an argument to the chain-spec-builder command updated in Joystream/joystream#1190

[shamil-gadelshin]

I recommend separating the exporting tool from the api-examples. A new repository would be a better choice.
Also, please make the API URL configurable.

[mnaamani]

code moved to new repo: Joystream/runtime-state-export-tools#1