BigNumber configuration seems to rely on npm deduping

[koirikivi]

The shared BigNumber configuration in utils/src/bignumber_config.ts seems to configure whatever BigNumber is installed as a dependency for 0xproject/utils. Note that this is not necessarily the same BigNumber as the one used by the caller.

I recently ran into an issue where schema validation failed for API calls made by 0xproject/connect because the BigNumber used by connect wasn't configured correctly (Order salts were serialized in the exponential notation).

Running npm dedupe fixed the issue, so I'm inclined to believe that this was because the BigNumber that was configured by utils wasn't the same as the one used by connect.

Possible fixes:

• Move bignumber from dependencies to peerDependencies in 0xproject/utils
• Instead of having a bigNumberConfigs.configure method in utils, just configure and re-export BigNumber and import it from utils instead of bignumber.js in the other packages.

Related to #293

[dekz]

I like the idea of exporting a configured BigNumber in utils package.

@fabioberger thoughts on this?