fix #1355 update SynEvents browser detection

The SynEvents util had an obsolete browser detection.
It has been removed and the `aria.core.Browser` one is used.

close #1355 and #1356
fix Messages in ErrorListWidget were inevitably escaped.

Now there is an option in the messages objects passed to the widget which controls how the message is escaped when displayed by the template.

Closes #1357
fix #1354: Overlay on section not properly disposed when refresing parent section