Description
Implements custom date expiration for AccessTokens and Hmac Tokens leveraging the expires column within auth_identities table.

Implements setIdentityExpirationById() model method, updateAccessTokenExpiration(), removeAccessTokenExpiration(), isAccessTokenExpired(), hasAccessTokenExpiry(), updateHmacTokenExpiration(), removeHmacTokenExpiration(), isHmacTokenExpired(), hasHmacTokenExpiry() trait methods and the CLI command shield:hmac invalidateAll.

Implements and closes #926

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide