better wording for pass phrase selection

_Originally posted by @tomholub in https://github.com/FlowCrypt/flowcrypt-ios/pull/323#discussion_r654560188_

```diff
-"setup_save_pass_locally" = "Store pass phrase locally";
+"setup_save_pass_locally" = "Save pass phrase";

-"setup_save_pass_in_memory" = "Keep pass phrase in memory";
+"setup_save_pass_temporarily" = "Remember pass phrase temporarily";
```