Implemented several changes to comply with OpenID Connect Core
Implemented several changes to comply with (OpenID Connect Core)[https://openid.net/specs/openid-connect-core-1_0.html]. Nonce validation changed such that it now verifies that the nonce and state associated with an LTI Message Launch request matches the state associated with the nonce and state created during the OIDC login request. Improve how line items are fetched and created when putting a grade to a line item.
For more details, see the changelog: https://github.com/packbackbooks/lti-1-3-php-library/blob/master/CHANGELOG.md#500
For information on upgrading from 4.* to 5.*, see https://github.com/packbackbooks/lti-1-3-php-library/blob/master/UPGRADES.md#40-to-50