merge of library encoders into SDK

[evias]

Issue scope

The nem2-library-js src/coders/ classes must be merged over in the SDK.

This merge will need a new folder src/core with utils or format subfolders for the encoder classes.

References :

• src/coders
• Merge features from nem2-library-js into reference SDK #61 : Merge of Library & SDK
• [Elephant] Use catbuffer for Schemas and Buffers generation #92 : use Catbuffer for Schemas and Buffers