Revise import-entry to transform instead of reject entries with inaccessible content

[jfroelich]

For example, instead of rejecting all nyt articles due to paywall, instead retain the entry and replace its content with a message that it is inaccessible (and a link to view the original).

For that matter, no user will ever be modifying the inaccessible hostnames list. It might as well be hardcoded within import-entry itself. Moving it to config was a mistake.