Adds oldest, latest methods to QueryBuilder, fixes #790

[yubarajshrestha]

fixes #790

[josephmancuso]

I don't really like the order by raw solution here. If we do the order by raw it won't work with postgres or sql server

for field in fields:
    self.order_by(field, "desc")

[yubarajshrestha]

I don't really like the order by raw solution here. If we do the order by raw it won't work with postgres or sql server

for field in fields:
    self.order_by(field, "desc")

Updated to order_by.

[BSN4]

tests?

[josephmancuso]

This looks better but will need some tests to make me feel comfortable with it

[yubarajshrestha]

This looks better but will need some tests to make me feel comfortable with it

Done

[yubarajshrestha]

This looks better but will need some tests to make me feel comfortable with it

Done