Fix PHP 8 compatibility issues

[omarabuhussein]

Before

Trying to create new event on PHP 8 sites throws an error:

After

Event creation page works fine:

Technical notes

This PR is built in top of the other PR here: #53 that regenerates the civix file so it can work with PHP 8 sites, but this is not the whole story, where when trying to access the event creation page it throws an error as can be seen on the "before" section, and the following error will show in logs:

Error: Non-static method CRM_Gotowebinar_Utils::isCiviCRMVersion47() cannot be called statically in CRM_Gotowebinar_Utils::getItem() (line 127 of /var/www/default/htdocs/httpdocs/sites/all/civicrm_extensions/uk.co.vedaconsulting.gotowebinar/CRM/Gotowebinar/Utils.php)

which happen because some parts of this extension code tries to access this method CRM_Gotowebinar_Utils ::isCiviCRMVersion47 statically , but the method itself is not a static method, which is no longer allowed in PHP 8.

In this PR I changed this method along with the rest of the methods inside CRM_Gotowebinar_Utils class to be static, given they are all called statically within this extension code.

I also removed a call for a class that does not exist in CiviCRM codebase CRM_Finance_BAO_Import_ValidateException and replaced it with CRM_Core_Exception.

[mlutfy]

I removed the "reviewed" status from civicrm.org, so that people do not accidentally break their installation (https://civicrm.org/extensions/gotowebinar-integration-civicrm-events) - I'll be happy to add it back when a new release it tagged.