Account for more field type aliases

[matthew-white]

odkmeta uses XLSForms, not XForms, and it looks to the XLSForm type when creating the do-file. For example, it correctly processes datetime, start, and end fields in the same way, knowing that they all correspond to the dateTime XForms type. However, there are other XLSForm types that we don't account for, even if it'd be easy to do so and we already have logic for the corresponding XForms type. We should look at the XLSForms alias.py and see if there are more field type aliases that we could easily incorporate into odkmeta.