Add event for new coins created

[alpe]

Emit event for dso_token instantiate with attributes for name, symbol, decimal and whitelist_group

[ethanfrey]

For dso_token::instantiate.

Maybe we can add this to cw20-base??

{
  "type": "create_token",
  "attributes": [
    {"key": "name", "value": "Liquid Gold"},
    {"key": "symbol", "value": "GOLD"},
    {"key": "decimal", "value": "6"},
    {"key": "allow_group", "value": "tgrade123456789"},
  ]
}

[ethanfrey]

Let's do this for v0.2.1 (point release)