[Enhance] EMAHook support does not load checkpoint strictly (#352)

* BaseAveragedModel support load ckpt without module prefix

* refine docstring

* allow EMAHook does not load ckpt strictly

* add unit test for strict argument of EMAHook

* sync remote

* sync remote

* clean the code

* ema hook supports setting start iter

* fix unit test

* fix as comment

* fix as comment

* describe kwargs