Enable old readers to access unencrypted columns in files with plaintext footer

[asfimport]

Reporter: Gidon Gershinsky / @ggershinsky
Assignee: Gidon Gershinsky / @ggershinsky

PRs and other links:

• GitHub Pull Request #106
• GitHub Pull Request #109
• PR

_{Note: This issue was originally created as PARQUET-1419. Please see the migration documentation for further details.}