Fix minor issues on the Resize dialog
Retrieve pixel encoding from image files

This will be helpful in the future if I decide to build my own RAW
editor, for custom-tweaking high-bit-depth files...
Add fail-safe termination for long-running metadata parsing

Sometimes ExifTool will inexplicably hang while parsing metadata, which
in turn freezes PD while it waited for the rest of the metadata to
arrive.  Such waiting will now terminate after four seconds without a
response.  (It's a bit long, I know, but on older machines it may be
necessary to wait that long for RAW images with messy maker-specific
binary metadata.)
Add "and contributors" to Copyright in About dialog, README

Obviously contributors retain all copyright to their code, so I should
really point that out when applicable...