add filter_format to morlet_filter_bank_2d whitelist
fix wavelet_2d bug when filter_format is fourier
make conv_sub_2d take 'fourier' format filters - lowpass + downsample for lower res
fix low-resolution behavior for high-frequency filters - lowpass before downsampling; only for formats 'fourier' and 'fourier_multires', 'fourier_truncated' is still broken
make inverse_wavelet_1d handle x_resolution parameter
speed up inverse_scat by reconstructing lower-frequency coefficients at proper resolution