Save and load cached pages with UTF8 encoding

Though TVTropes uses ISO-8859-1 encoding, encoding cached page
HTML as ISO-9959-1 (NSISOLatin1StringEncoding) does not allow
pages to be saved properly. Saving and loading pages with UTF8
encoding appears to cause no encoding issues.
Change SavedPagesController to load data synchronously

With HTML data stored in filesystem rather than CoreData, no need
to drop cached data and reload asynchronously when switching
between SavedPagesController tabs. In the future, should load data
asynchronously only once on viewDidLoad.
Fix saving random page triggering segue