Radial coefficients k1, k2 hard-coded to zero when reading values

So currently we have k1 and k2 hard coded in different I/O reading files, and as default for EXIF:

https://github.com/borglab/gtsfm/blob/master/gtsfm/common/image.py#L68
https://github.com/borglab/gtsfm/blob/master/gtsfm/utils/io.py#L189

They are also hard-coded to zero when resizing intrinsics. Since they are coefficients of polynomials, a linear rescaling shouldn't be sufficient, though.