Import scope for table configs, especially for iterators to validate k/v

Recommend adding an "import" scope to the table configs, including the ability to set iterators for k/v validation during bulk import.

Scenario: Administrator fails to change to the proper table when executing the importdirectory command from the shell. Instead of an avalanche of scan and compaction failures due to unexpected row, colf, colq, and visibility formatting, the import scope's iterator stack rejects the offensive key/values and maintains the integrity of the table.

Could happen? Definitely happens! Even a simple regex iter in such a scope could prevent a lot of heartache.