Pass phrase dialogs called during backup checks aren't working properly

[rrrooommmaaa]

Following PR #3973
The code logic in encryptForBackup() method (formerly inside backupOnEmailProviderAndUpdateUi()) activates passphrase frame by sending passphrase_dialog message to the hosting page. The passphrase frame is shown ok, and after its completion (waitUntilPassphraseChanged call), the backup procedure was supposed to continue. However, this never happens as the passphrase frame seems to wipe out the backup frame (probably because they are both set up with Ui.modal.iframe that doesn't expect to keep more than one). So the backup procedure terminates without a proper warning, and the test settings - manual backup a key with a missing pass phrase is by now incomplete.

[tomholub]

Reading all of these backup related issues makes me think we should be forwarding from frame to frame to frame like that.

Should instead have a backup library that renders the appropriate UI in whatever frame you are. Similar issue #2663

[tomholub]

Maybe this could be fixed now, after a refactor that was done?