Remove hard coded divisors

[markbeazley]

There are a few Sylius users who store their prices at a different prescicion to the Sylius default, and need to use a different divisor when converting to and from the int price value, to allow for easier overiding of this divisor the IntToStringConverter and DivisorProvider services should be used instead of hardcoding the value of 100, allowing stores that use a different divisor to only override 1 small class instead of quite a few different classes across the plugin.