Comply with the lightweight ownership standard ERC-5313

[jaybuidl]

Motivation

Currently we are exposing the contract owner using the governor() view function.
However it is not a standard practice and some tools expect to find an owner() view function for ownable contracts.

Solution

The ERC-5313 requires only an owner() which would be trivial to follow.

This ERC is in FINAL status.

Alternatives

There is the older and heavier ERC-173 standard which requires implementing ERC-165 and a transferOwnership() function with an event. ERC-5313 is a subset of ERC-173.

Another alternative is OpenZeppelin's Ownable which is even heavier (e.g. depends on another Context contract). Ownable doesn't implement ERC-165 and is therefore not ERC-173 compliant.