Replace ComicBookSummary with CBS summary instances
Move Model.IsSummary to Item; add checks

These checks prevent a summary from accidentally being persisted or
retrieved.
ISearchPersistence<T> implement IPersistence<T>

This required constraining ISearchPersistence<T>'s T to be a Model.
Remove Item-specific interfaces

Replaced with improved ISearchPersistence<T> interface.
Replace PImport/PExport builders w/ IoC container