Add two hooks to plugin-page.php

[Mofect]

I have added two hooks for adding admin page header and footer in view/plugin-page.php In some situations, the theme authors want to integrate the demo import page to their own admin page or add their own admin top menu to the demo import page, so they can use add_action() to do that easily without making a wrapper plugin to include this plugin again.

[primozcigler]

Thank you @Mofect for your contribution! 🙏