Refactor of tokenization and detokenization within the NMT model
This pull request **introduces 4 alerts** and **fixes 1** when merging ae81427bba749fe8dd90229c958aef151bd8aa33 into cc4bfc06993326fcd8bb978460754b89026341ff - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-257f9409c9404fe2fe6c2d87d34dc968e99b8e1c)

**new alerts:**

* 4 for Unused import

**fixed alerts:**

* 1 for Unused import thank you for doing this. lgtm. This pull request **introduces 4 alerts** and **fixes 1** when merging 9193ed5c9dd5a6002c2c366556783ee68978a825 into 1b82b571c2f32e1b109677a67c5820222cb696fe - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-80bd0bb0142abf15d8bcf3404d2ff85ea5ab25cf)

**new alerts:**

* 4 for Unused import

**fixed alerts:**

* 1 for Unused import This pull request **introduces 1 alert** and **fixes 1** when merging ed75070f3ba732944f4ae09ac6c913ba5da3470d into 1b82b571c2f32e1b109677a67c5820222cb696fe - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-d3199dbf754c721c131a5e33985cad4ea3fb9ef1)

**new alerts:**

* 1 for Unused import

**fixed alerts:**

* 1 for Unused import This pull request **fixes 1 alert** when merging b761630ea0b35facb77865e3b126cb958b374740 into 1b82b571c2f32e1b109677a67c5820222cb696fe - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-53e715d1d4bfc01e223032c2575b07bbda2109b5)

**fixed alerts:**

* 1 for Unused import This pull request **fixes 1 alert** when merging 843d255e3f9d52e4cc09ad220c9986c80adb0342 into 1666139b6b3334dc8f699f69d5a97aec4fe53419 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-5fda55ea2dcf9960b6efde9acea83ddbabad54fa)

**fixed alerts:**

* 1 for Unused import This pull request **fixes 1 alert** when merging e3ec54b607ed63a44cd55b867876eecb310ec34c into 2e9e5b174ed3b766abbd6bb89b9d2c96e5d8f66c - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-5e15a729fe2d136a97e9b121d1cb6b589edb1016)

**fixed alerts:**

* 1 for Unused import Lgtm. Thanks again!
This PR refactors some of the fetching of tokenizers, normalizers, and detokenizers within the model and creates Chinese/Japanese tokenizer and detokenizer classes to match Moses semantics.