Consider indexing name argument in all Vouching events

[tinchoabbate]

@spalladino suggested in PR #115 indexing name arguments for all events fired in the Vouching contract.

I'm moving the discussion outside the PR so it can be better documented.

Related issues were the problem of indexing string arguments has been discussed:

• in OpenZeppelin
• in zOS

[spalladino]

Following the discussion in OpenZeppelin/openzeppelin-contracts#992, it'd seem like the best course of action would be to make name indexed in all events, and add a fullname unindexed argument in DependencyCreated. WDYT?

[tinchoabbate]

Reviewed the comment you left in the PR, and I've been working locally on a new implementation that addresses them in some ways.

Quick question, do we need the name to be a string? Could it instead be a bytes32? In my tests I'm seeing that (as you mentioned in the PR), bytes32 indexed event arguments are not being hashed. Furthermore, it seems that only fixed-size types can be indexed (see trufflesuite/truffle#405 (comment)).