Extends Piped into the past if Total Improve exist #2360

This is required for Iraq
Allow reference to current year in formula #2360

This allow us to code exceptional cases depending on the year. This
was required to solve exceptional case of Tunisia rural Open Defecation.
Custom rule for Saudi Arabia #2360

We use a variant of standard formula, but drop the extension in the
past so we can extends in the future based on 100% - Improved+Shared.
This needs to be done in order to avoid values going from Open Defecation
to Other Unimproved in 2003-2005.