Add the ability to show and process a crawler error log

[bhermann]

As crawlers operate in the shadowy background, we need some way to know if there were problem processing work items. In order to show then, add an error log to the elastic search database that can be processed inside the management application.

Processing can include:

• Viewing the error log
• Marking entries as complete and removing them from the log
• (nice to have) pushing a work item back on the queue