Returns the absolute path to the qooxdoo framework used by the current project, unless
the user provided a CLI option "qxpath", in which case this value is returned.
@return {Promise(String)} Promise that resolves with the absolute path
async function() {
      let qxpath = await this.getAppQxPath();
      return path.isAbsolute(qxpath) ? qxpath : path.resolve(qxpath);
    }