Fix bugs with caching and format validation when importing files#204

Fivell merged 2 commits intoactiveadmin-plugins:masteractiveadmin-plugins/active_admin_import:masterfrom

Skumring:Fix-bugs-with-caching-and-format-validation-when-importing-filesSkumring/active_admin_import:Fix-bugs-with-caching-and-format-validation-when-importing-filesCopy head branch name to clipboard