[tracking] List of size optimizations for Agent JS

[hansl]

This is a grocery list of various optimizations to get the size of packages in this repo down.

• [x] Harmony imports #251
• [x] Change package.json according to this blogpost
• [x] Replace Buffers with ArrayBuffer #245
• [ ] Remove CRC32 (which depends on Buffers) #267
• [ ] Remove dependencies from third party libraries #222
• [x] Replace BigNumber usage with BigInt #269

Other tasks related to size optimization;

• [ ] Add CI step to report size changes in identity-provider #229
• [x] [Tracking] Separate Candid into its own packages (and move to candid repo) #276