Removed old Doctrine 2 talk, added Models & Service Layers

Hi folks,

Great work putting this list together! I took the liberty of removing an old talk that probably isn't relevant or even best practices anymore.

I also added a more recent talk, both as a video + slides (not sure which is preferred). Couldn't quite settle on where it belonged so moved it into a service layers section. Obviously feel free to move it around or revert the addition, I just wouldn't want an old talk to mislead someone. :blush: 

Thanks!