taxonomy: support for changing type of the terms/properties

[yogeshVU]

Currently there is support for renaming the term/fields with different value.
However, there is a lack of support for changing a type of a given field.
For instance, in a recent update to one of the vocabularies, there was a need to change the type of the field from "Boolean" to "Enum". The renaming allows the changing the field name, but not able to cover the type change requirement.