Allow blockchain download/ingest before user clicks "OK" on encryption warning

[imnotpete]

When thought-qt first starts up, while the splash screen is still displayed, a warning is presented to the user to ensure they encrypt their wallet for security.

The blockchain download/sync/etc process doesn't begin until this warning is clicked away by the user.

It would be helpful if that blockchain process could begin immediately, while the app is waiting for that confirmation. Otherwise, there are cases where a wallet is started just before walking away for the night, for example, only for the user to discover in the morning that it did not start the chain update.