Visibility of synchronization errors

When doing a background synchronization, the Thunderbird connector reports progress as status bar messages (remember that _OBM Sync - Done_ message in there ?).
As a reminder, the connector does a background sync in the following situations:

* When an automatic synchronization interval is configured.
* When _proactive synchronization_ is enabled and a change is detected by the connector ([details](http://obm.org/blog/new-features-thunderbird-connector)).

Starting with version 3.2.0.4, the connector can now be configured to report errors during background synchronizations in a modal alert box. This means that:

1. Until the alert is closed (meaning that the error was acknowledged by the user), no other background synchronizations will run.
2. While the alert is open, the Thunderbird user interface isn't usable. This forces the user to acknowledge the error and take any necessary actions.

## How to use

To enable this new behavior, please set the preference _extensions.obm.backgroundErrorMustBeAcknowledged_ to __true__ using Thunderbird's config editor.Buty Nike Damskie Wyprzedaż