move last parts of import logic from kis into operation

OpenKeychain/src/main/res/values/strings.xml

@@ -1021,6 +1021,7 @@
     <string name="msg_import_fingerprint_ok">"Fingerprint check OK"</string>
     <string name="msg_import_merge">"Merging retrieved data"</string>
     <string name="msg_import_error">"Import operation failed!"</string>
+    <string name="msg_import_error_io">"Import operation failed due to i/o error!"</string>
     <string name="msg_import_partial">"Import operation successful, with errors!"</string>
     <string name="msg_import_success">"Import operation successful!"</string>