WP - Errors after update from 4.6 LTS to 4.7
This is highly due to one of the custom extension enabled on your site. Few steps you could try to fix this -


Check if any of the extension overrides the file CRM/Core/Config.php. If you find it, move it outside the site dir and disable that extension after reloading the page.
Manually disable the extension from the database one by one and try to reload the page. To disable the ext, set is_active value to 0 in civicrm_extension table. (Remember to revert it back if the page reload is still an error).
Check if the custom php directory overrides the core file CRM/Core/Config.php. If yes, do the same as step 1.