Improve data provider consistency checker and repairs

[prioux]

Several issues:

• repairs not started in background, long repairs block the rails instance
• too many entries for the same type of errors, maybe regroup them
• filter/group errors by type of errors (instead/as well as) 'severity'
• a completely empty directory configured as a remote EnCbrainSshDataProvider still generated an error with Unknown entry " (double quote)
• fixes should operate with batch arguments instead of one entry at a time