Clear the password field in case of incorrect password entry

[Pythonix]

Currently, after the notification that the password entry was incorrect, the password must be deleted manually. This PR will automatically delete the password.

[threema-danilo]

Thanks! That makes sense.

However, it would feel more natural if the password is cleared when the error dialog is closed. Could you change that? In showDecryptionFailed, you can add an onRemoving callback to the .show()-arguments:

this.$mdDialog.show({
    ...
    onRemoving: () => { this.clearPassword(); },
});

(Untested)

[Pythonix]

Thanks, I adopted your suggestion and tested it. Works as intended.

[threema-danilo]

Thanks! Looks good now 🙂