Handle scancode output files that include --only-findings

[steven-esser]

Originally reported here: #393

When a scancode results file has the --only-findings option present, data gets loaded into the database but the Tree View itself does not get created properly.

scancode-workbench should support the proper loading of scans that include the --only-findings option.

[steven-esser]

The main problem with this data is how the JSTree tries to render it. It cannot render things correctly when parent/child files and directories are arbitrarily placed (which is the case with --only-findings).

This may also be an issue when attempting to implement #355, depending on the approach.