Add banner image as a special `IdentityImage` beside "thumbnail" and "large"
Banner input cropped image processing
- Resize to keep in the limits of `BannerDim`
- Encode to match the file size limits define for banner
- Don't scale up. This can be done efficiently in the UI
Changes to `images` module
- Refactor `EncodeToBestSize` as `EncodeToLimits` to accept arbitrary dimensions
and allow for custom size
- Define `DimensionLimits` for banner not to exceed 450 KB and a rough estimate
for the ideal size
Stefan