Update autoloading and setup discussions for composer

[weaverryan]

In several documents, such as the_architecture and symfony1, we talk about things like autoloading and show autoload.php. With Composer, this changes in two ways:

• The actual autoload paths look different, since libraries are installed into different locations. Much of this was updated in [Composer paths] Updated paths that are now created/managed by composer #1165, but we still have pasted versions of the old autoload.php as examples in some places
• The conversation itself needs to be altered - autoloading is important, but now handled by composer

[Sgoettschkes]

I'm on it!