Job properties expression

Ability to perform basic arithmetic operations for the props. Uses Jexl.
Simply, the mechanism uses $(...) for any resolution. i.e key=$(x + y)

Cool things you can do:
Variable replacement occurs before expression handling, so you can use azkaban's variable replacement.
i.e. 
key=$(10 + ${my_value})
my_value = 1
// resolves to 11

Or even nest or replace queries:
i.e.
key=$(10 + ${my_expr})
my_express=$(10 * 2)
// resolves to 30. This is equivalent to $(10 + $(10*2)) or $(10 + (10*2))

And do other funky stuff:
key=$(5 * 10) degrees
// resolves to '50 degrees' string