Allow to set genesis_accounts in ae instead of aettos

[davidyuk]

Currently, to create an account with 1000ae, I'm using

chain:
  genesis_accounts:
    ak_21A27UVVt3hDkBE5J7rhhqnH5YNb4Y1dqo4PnSybrH85pnWo7E: 1000000000000000000000

would be good to avoid managing 18 zeroes somehow. For example to use scientific notation, like

chain:
  genesis_accounts:
    ak_21A27UVVt3hDkBE5J7rhhqnH5YNb4Y1dqo4PnSybrH85pnWo7E: 1000.0e18

The problem is that the balance is parsed as float and gets rejected by the node

node-1      | 04:54:12.658 [info] Reading config file /home/aeternity/node/aeternity.yaml
node-1      | 04:54:12.666 [error] Validation failed, Pos: chain/genesis_accountsak_21A27UVVt3hDkBE5J7rhhqnH5YNb4Y1dqo4PnSybrH85pnWo7E | Value: 1.0e23 | Schema: {"description":"Token amount","type":"integer"} | Reason: Wrong type
node-1      | 04:54:12.666 [error] aeu_env:read_config()-> ERROR: validation_failed

The node may accept both integers and floats but ensure that the float can be converted to an integer without rounding.

Alternatively, the node may accept a specially-formatted string, like

chain:
  genesis_accounts:
    ak_21A27UVVt3hDkBE5J7rhhqnH5YNb4Y1dqo4PnSybrH85pnWo7E: '1000ae'

However, it won't be compatible with custom chains that may use a different name and/or denomination.