Fix moving a unique_ptr<const> to a shared_ptr<const>.

gcc 4.6 doesn't like it even though it should be allowed.
Start writing the interface for the new Session/View architecture.
Starting moving file functionalities from CrawlerWidget to Session.
Move the responsibility of creating the LogData to the Session...

... from the CrawlerWidget.
Use the list of files in the Session.
Cleanup the starting sequence.
Implement a signal multiplexer between the MainWindow and the
CrawlerWidget(s).
Correctly implement Reload.

Now reload instead of loading again in a different crawler.
Move stopLoading back to the CrawlerWidget, next to reload.