Bug933963 split up signature summary

Splits up the gigantic update_signature_summary() empire into: 
```
update_signature_summary_architecture
update_signature_summary_device
update_signature_summary_flash_version
update_signature_summary_installations
update_signature_summary_os
update_signature_summary_process_type
update_signature_summary_products
update_signature_summary_uptime
```

I also introduced `backfill_named_table(tablename, date)` function! This primarily affects DBAs or people who are running backfill manually to fix old data.

Crontabber doesn't use backfill_* functions, so this shouldn't affect production activity. The idea is to eliminate the need for specific `backfill_foo` functions in the future.  I need to audit all existing functions before I can fully deprecate old backfill functions. I have audited all the signature_summary functions affected by this patch and they can all be safely used with `backfill_named_table()`.