Add keys, values, pairs, invert, pick, omit, each, and other
underscore methods to models
Merge pull request #2040 from akre54/add-underscore-methods-to-model

Add underscore methods to models
Revert "Add keys, values, pairs, invert, pick, omit, each, and other"

This reverts commit faa776a67cdaa674fd8da596f62e8028f371e2c9.