Update underscore.js to official 1.4.4 build

- needs shim, previously we used the modified version from
Update backbone.js to official 1.0

- options constant for Collection.add() needs to be modifiable, because
backbone merges in default options (like add:true)
Revert "Update underscore.js to official 1.4.4 build"

This reverts commit 83b3b00eaa90a6ce63d89ad1b0927cfac663b0b7.
Update underscore.js to AMD 1.4.4 build

- need to use this version so the opt build still works (couldn't find
"_" with the official build + shim)