Status output for importswid command
Removed encoding argument from prettify_xml

Input to the function should always be unicode. The assumed output
encoding is alwalys UTF-8.
Add tag-file relations in chunks

SQLite does not allow more than 999 parameters to be present. When
adding more than 999 files to a tag using `tag.files = [...]`, it will
fail with an OperationalError.

This commit adds chunking to the `process_swid_tag` function. The
TagFile instances are created in bulk using chunks of 950 items.