Data type creation - names

[PhilipSkinner]

The user should be forced to enter a name for a data type when they create it - and they should not be able to update it once it has been entered.

This is to stop renaming of data types - doing so creates a new table and has no mechanism for migrating of data.

It should be possible to rename datatypes in the future - but renaming of datatypes is a more involved thing as it means having to scan and fix all things that may reference the datatype by its name.