Revert "Operations with ReadOnlyFolderException are unrecoverable"

This reverts commit 2ca0ec64ad.

app/src/main/java/eu/faircode/email/Core.java

@@ -90,7 +90,6 @@ import javax.mail.FolderNotFoundException;
 import javax.mail.Message;
 import javax.mail.MessageRemovedException;
 import javax.mail.MessagingException;
-import javax.mail.ReadOnlyFolderException;
 import javax.mail.SendFailedException;
 import javax.mail.Session;
 import javax.mail.Store;
@@ -262,7 +261,6 @@ class Core {
                                 ex instanceof MessageRemovedException ||
                                 ex instanceof FolderNotFoundException ||
                                 ex instanceof IllegalArgumentException ||
-                                ex instanceof ReadOnlyFolderException ||
                                 ex.getCause() instanceof CommandFailedException) {
                             Log.w("Unrecoverable");