Consistent field mapping

The MapFieldOntoOutput implementations for the filters are often missing or inconsistent.

Let's refactor the implementations so that:

Any filter that modifies points should remap point fields.
Any filter that modifies cells should remap cell fields.
The worklet method that remaps point fields should be named ProcessPointField.
The worklet method that remaps cell fields should be named ProcessCellField.
The remapping fields should take an input ArrayHandle and DeviceAdapterTag and return an ArrayHandle<ValueType> with default storage (no fancy array handles), e.g.

template <typename ValueType, typename StorageTagIn, typename DeviceAdapterTag>
using MapSignature = ArrayHandle<ValueType>(const ArrayHandle<ValueType, StorageTagIn>&,
                                            const DeviceAdapterTag &) const

Questions:

If a filter doesn't modify points, should DoMapField return false or pass the input through and return true?
Does the proposed signature capture all of the possible data needed for remapping? (Policies, etc?)
Should the output storage type for mapped fields match the input, or use the default storage?

Current state of the filters:

Edited Jun 21, 2017 by Allison Vacanti