Add "new" option

[richard-uk1]

When working on an existing saved term set, it is not possible to start again on a new term set. This is a problem if the user wants to create multiple named term sets in a single session.

[rw251]

Agreed. My current workaround is just to clear all the codes and refresh the page.

[richard-uk1]

The name is bikesheddable. I suggested "new" because that matches e.g. MS Office. Other possibilities are things like "clear".