The "Test with file" function should auto re-parse the file when a row is selected in "Use as"

[Nicklas Nordborg]

When you select a row to "Use as=Data header" for example, the only logical action that follows is to re-parse the file to allow for column mappings. In the current implementation the "Parse the file" button must be clicked manually. It would be nice if the file was re-parsed automatically.

[Nicklas Nordborg]

In 7660:

Fixes #2163: The "Test with file" function should auto re-parse the file when a row is selected in "Use as"