loadFile(file) {
        const self = this;
        const ext = path.extname(file.name).toLowerCase();
        return this.isZip(ext) ? self.processZip(file) : self.processFile(file, ext);
    }
Import Step 1:
Load the given file into usable importData in the format: {data: {}, images: []}, regardless of
whether the file is a single importable file like a JSON file, or a zip file containing loads of files.
@param {File} file
@returns {Promise<ImportData>}