Apply spatial filtering to undersampled data in coron3

[stscijgbot-jp]

Issue JP-3627 was created on JIRA by David Law:

Per input from Marshall Perrin 

"A step which exists in spaceKLIP, and likely could/should be added to coron3 is a spatial filtering step applied to spatially undersampled data. For wavelengths at which the PSF is not Nyquist sampled, empirically it reduces numerical noise to apply a blur kernel to slightly smooth the data prior to interpolation and alignment."

Setting to 'On Hold' for now to save the information for future consideration.