Fixes #1470 & #1488

Files should only be added to the CACHE section & not have a hash in their file name.
#1470 Hashed filenames are confusing all versions of Safari
#1488 Each static resource is being downloaded twice when appcache is enabled 

Changes:
* Remove resource.hash being added
* All files in public are only added to the CACHE section
* Fallback can be empty in the current implementation.
* app.manifest on L156 removed because it is not necessary
* adding opera to knownBrowsers & browsersEnabledByDefault, because the new version seems to need it.

[Detailed explanation & example repo](https://github.com/akralj/meteor-appCacheSafariBug)