Prorate new employees

[BlinkVonDoom]

closes #78, closes #76, closes #77

test plan : -upload user tables with start_date being in current year, but past date.

• make sure one user has a start date 90 days (3 months) from Date.today

New users should have lower than 180 bank_value according to 180-(180*(user.start_date/YYYY-12-31))

After users are imported their values should reflect the new value.

new users with start_date < 3.month should have on_pip = true

• run rake new_hire_check_pip check user from above that had start date 3 months in the past, their value should now be on_pip = false

[merchang]

closing pr because all commits exist in #83 Agent.csv refactor required prorating logic