Fixed URL sent out in event creation LVAlert to a valid URL, namely the URL of the event file in the web interface.

Fix for Issue #975, 'Versioned files displaying only newest versions in event detail page'. To fix this, we add a file_version field to the event log. This is accessed from the VersionedFile object at the time of file-saving. That way, the correct version can always be associated with any given log message.