Define groups

[ethanfrey]

A first step towards #80

• Write cw4 spec and helpers
• Write cw4-group contract and raw queries (test raw queries)
• Update READMEs with final interfaces

Later:

• Write cw3-flexible-multisig querying a remote group contract (with smart or raw queries)
  • no need to write special admin for multisig, it can relay the "UpdateAdmin" message like any other CosmosMsg, the groups module enforces permissions on receipt
• Write integration tests for cw3-flexible-multig as part of Test harness for testing composition #9
• Write init script to set up 2 multisigs pointing to 1 group, with one multisig as group admin as part of Define message callback as cw spec #98