FameTheme Demo Importer

Medium risk: 1 removed function, 1 method signature change, 1 removed asset handle.

• The function demo_contents_custom_upload_xml() was removed. Direct calls from a theme or another plugin will fatal.
• Demo_Contents_Progress::resetup_repeater_page_ids() now requires more arguments than before.
• The script/style handle demo-contents is gone. Code that dequeues, or declares a dependency on, that handle is now wrong.
• New external hostnames appear in this release: design-library.pressmaximum.com.