User register template: check if site-wide privacy statement is enabled

[Vitaliy-1]

Templates from the current master branch of OJS and themes

1. This condition checks if there is any site-wide registration info entered in the form but similar call in registrationFormContext.tpl checks if the setting is enabled in the config. The former could be changed to: {if $siteWidePrivacyStatement && $enableSiteWidePrivacyStatement} for consistency. If a user disables site-wide privacy statement from the config, it will nevertheless appear on the sitewide registration page if the data to the correspondent form was previously entered from a dashboard.
2. Inputs for sitewide registration are now situated in 2 places: registrationFormContext.tpl and its parent userRegister.tpl: https://github.com/pkp/pkp-lib/blob/master/templates/frontend/pages/userRegister.tpl#L125-L164. My proposal is to move all that data to the former template, to keep it in one place.