Fixed iterator helper node type persistence

[RunDevelopment]

Fixes #838.

The manual output types for iterator helper nodes caused problems because they can be out-of-date easily. Since these nodes do not have any inputs, their input hash never changes and so the manual output type is never reset.

This PR fixes this issue in 2 ways:

1. Iterator helper nodes with an "Auto (Iterator)" will now "inherit" the input hash of the parent iterator. This causes their input hash to change whenever the parent iterator changes.
2. useOutputData now explicitly return the last and current output. This difference makes it impossible to accidentally display/have types of old output data.