Removed [*]RenderQueue::AddModel
RenderQueues now use std::map::insert only if necessary

It looks like my std::map::insert implementation allocates something,
even if the element is present (It's not a leak, just some useless
allocation)
Optimized String usage

It will no longer initialize the buffer if not necessary
Fixed sprite rendering in Deferred Shading

Temporary fix: In the future Deferred Shading shall work with some
sprites
Fixed potential overflow in OBJ Loader
Improved Scene implementation

Will provide a default background/technique when necessary