Integrate Liger

[lapp0]

https://github.com/linkedin/Liger-Kernel

Should be easy with linkedin/Liger-Kernel#242 (comment)

Also we should patch kl_div loss with ligers kl_div if liger is available.

[ByronHsu]

thanks :-)

[lapp0]

Integration complete, but awaiting linkedin/Liger-Kernel#272 because kl_div (and possibly other components) have broken grad computation.