Reject space before filename with folders

@iwehrman - For issue #227 

If the layer filename is of format: [folder]/[whitespace][filename]…
parser throws an error, which gets logged to errors.txt.

Also update the unit tests so they call a unit test specific function
which catches the error thrown by parser so unit tests can check for
error messages. This needs to be refactored later to apply to all
parsing rules.
For consistency with the rest of the code, let's also include the `name` parameter. The `@returns` JSDoc should be updated too.