Use hazard_field and hazard_value_map for Hazard's Layer Keyword

[ismailsunni]

Problem

Currently, the wizard write the value of field and value mapping of hazard in field and value_map key in layer's keywords. It's not explicit.
Meanwhile, in exposure layer, we use exposure_class_field. Which is very explicit.

Proposed Solution

Use hazard_field and hazard_value_map to replace field and value_map respectively.

Notes

This is low priority.

[ismailsunni]

Do it last. Since it won't be seen by the user. And after the change, I need to update the keyword in test data (which is painful :) ).

Moreover, may be we won't do anything since we will migrate to metadata class.

[ismailsunni]

No longer valid for the current metadata.