Improve import capabilities

A set of proposed enhancements to the import capabilities.

1) Rewrites some reserved-word IDs, like "toc", in imported content, to prevent conflict with navigation items.

2) Adds an extracted page title to the content list for EPUB imports, replacing the manifest ID. This makes it easier to tell which content is which.

3) Adds a "part" content type selector to the import for IMSCC, and selects any modules as "parts" by default. When importing, any chapters following a part will get added to that part.  This should allow import from IMSCC retaining the module structure as a part structure.  Also removes the <pre> formatted var dump on module title content, since that isn't very useful.

4) Adds citation and licensing options on the content import content selection page, applying those selections to all imported content.  This will greatly simplify applying appropriate citation and licensing when importing whole books.

There's still a big TO-DO for imports around dealing with WRX imports, since that's our current only way to move content from one site to another. Currently part structure, citations, and licensing are all lost on import in WRX.