Added a name sorter

This commit reworks the sorting system, making it to sort
data as QVariantMap instead of items, that are most of the
time null.

It also adds a name sorter, to sort Facebook items that have
a name.
Added cover photo
Behaviour change, no request when no filter

This commit sets a new behaviour for empty filter.
There should not be any request when no filter is provided.
Bugfixes

Bug fix when having an empty model that causes crashes.
Debug informations