Merge pull request #503 from melissalinkert/gif-metadata

GIF: add a few more things to the metadata table
Remove TODO
merge develop -D org -I include -E exclude: PR 482 (Remove 2003fc and related classes)
merge develop -D org -I include -E exclude: PR 485 (Fix export of multiple files (rebased onto develop))
merge develop -D org -I include -E exclude: PR 504 (Prevent false positives in open file handle test)
merge develop -D org -I include -E exclude: PR 505 (Add MetadataRoot to MetadataStore getRoot/setRoot interfaces)
merge develop -D org -I include -E exclude: PR 506 (Memoizer: use Location instead of File to represent 'id')