Register constants in Smarty

[jonasraoni]

Describe the bug
A couple of constants are emitting the message Using unregistered static method "{$constant}" in a template is deprecated and will be removed in a future release. Use Smarty::registerClass to explicitly register a class for access.

Here's the current list:

PKP\components\forms\context\PKPThemeForm::FORM_THEME
PKP\components\forms\context\PKPRestrictBulkEmailsForm::FORM_RESTRICT_BULK_EMAILS
PKP\components\forms\publication\TitleAbstractForm::FORM_TITLE_ABSTRACT
PKP\components\forms\publication\PKPCitationsForm::FORM_CITATIONS
APP\components\forms\publication\SubmissionPaymentsForm::FORM_SUBMISSION_PAYMENTS
PKP\components\forms\publication\PKPMetadataForm::FORM_METADATA
PKP\components\forms\publication\PKPPublicationIdentifiersForm::FORM_PUBLICATION_IDENTIFIERS
\PKP\submissionFile\SubmissionFile::SUBMISSION_FILE_PROOF
APP\components\forms\publication\AssignToIssueForm::FORM_ASSIGN_TO_ISSUE
\APP\journal\Journal::PUBLISHING_MODE_SUBSCRIPTION

What application are you using?
OJS 3.5

[asmecher]

I'm hoping this will go away before 3.5.0 gets released -- see smarty-php/smarty#1028. (In other words, please don't work on this yet!)