Gabriel Staroň

### Bug Description TimeseriesForecaster predicting fails: Traceback (most recent call last): File "../ak.py", line 156, in predictions = clf.predict(pred_data) File "../__venv_ak__/lib/python3.8/site-packages/autokeras/tasks/time_series_forecaster.py", line 289, in predict return super().predict(x=x, **kwargs) File "../__venv_ak__/lib/python3.8/site-packages/autokeras/tasks/time_series_forecaster.py",...

1. Added support for multiple sheets. 2. Only 1 composite property for columns, data, sheetname properties. 3. Get rid of requiring jquery.