Add ImportedHitsFile#same_on_disk?

* Let the imported file check itself for difference
Allow a skippable job in ConsoleJobWrapper

* Use as start 'message' do |job|
* job.skip! will print the "skipped" message
* Returns true to enable "job.skip! and return"
Skip import of hits TSVs we have seen

* Keep track of what we've seen by using ImportedHitsFile to hash contents
* Don't reprocess things whose hashed contents haven't changed
Allow ConsoleJobWrapper to pass a return value

* Is the same value as the return value of the block to which it
  yields
Print number of files imported vs skipped/unchanged.

* In Transition::Import::Hits.from_redirector_mask!
Don't do expensive operations when nothing changed

* Don't refresh daily hit totals
* Don't refresh hits/mappings relations