This adds additional front and backend validations for task order file
names. We are now restricting file names to a whitelist regex of
[A-Za-z0-9\-_ \.] for simplicity.
Note:
On the frontend, the filename string must have at least one character.
This is not true in the backend validation; because of the way the
entire task order form is validated, requiring input would break the
business logic currently implemented.
