lower MTurk payment

[amyjko]

$0.25 is too much.

[mjslee]

During discussion, we thought this might be a good breakdown to test during our MTurk pilot:

Start: +$0.25
Each level: +$.05 or +$0.10

[mjslee]

Updated code so that it increments by 10cents per level. Depending on the results of the pilot, this will be adjusted before the full launch.