Price rules rehaul

[manycoding]

Refactor compare_was_now, compare_prices_for_same_urls, compare_names_for_same_urls, compare_prices_for_same_names

compare_was_now:

• compares numeric value between two job fields
• Outputs >, <, =

compare_prices_for_same_urls

• returns url field values difference between 2 jobs (new, same, missing)
• for same urls, compares price

compare_names_for_same_urls

• compares names for same between 2 jobs urls

compare_prices_for_same_names

• returns name field values difference between 2 jobs (new, same, missing)
• for same names, compares price

The last three do the same:

• find given field difference - can go in a separate rule
• compare certain field values between 'same' items. Items are found by a key, different from item_key (e.g. url/name)