Change resources loading method: load offline

[loicortola]

Today, each fragment handles their own content in a cache, and lazy-loads the views.
This has two drawbacks:

• 1: it takes time to load
• 2: in case connectivity is not great, this could result in a delay or simply black screen

The best way is to load all files completely offline when an update was made.
The diffs metadata gets loaded, then the payloads too.
After, the views only load the content from files.