[Gas Fix] move token serialize to mintShares

[dmvt]

Description

The token model is serialized in the join function and then again in mintShares. It would be cheaper to calculate lambdaDash and mDash in Token.mintShares. This avoids duplicate calls to Ecosystem.deserialize and to Token.serialize.

    // mdash
    uint256 lambdaDash = SafeMath.add(token.maxLambdaPurchase, token.lambda);
    uint256 mDash = ElasticMath.mDash(lambdaDash, token.lambda, token.m);

    // serialize the token
    Ecosystem.Instance memory ecosystem = _getEcosystem();
    Token tokenStorage = Token(ecosystem.tokenModelAddress);
    token.m = mDash;
    tokenStorage.serialize(token);

    // tokencontract mint shares
    bool success = tokenContract.mintShares(msg.sender, token.maxLambdaPurchase);
    require(success, 'ElasticDAO: Mint Shares Failed during Join');

Definition of Done

• mDash and lambdaDash calculations are in the mintShares function
• Token is not serialized in ElasticDAO.join