Fix Custom field date query builder to work with 'raw' high & low params

Fix Custom field date query builder to work with 'raw' high & low params

Once we convert to datePicker we will be passing in parameters like custom_3_high, custom_3_low & custom_3_relative.

Currently we pass in custom_3_to & custom_3_from and custom_3_relative. This adds support for the new high & low
withoutt touching support for previously working or switching the field across (as yet). This paves the way for
the datepicker conversion. After a lot of brain pain I concluded the fundamental problem was the whereTables
from the CustomQuery were being merged in but actually then lost when where() is called.