rethink & consolidate usage of BigInt / BigNumber throughout the SDK

[marc0olo]

known related issues / PRs:

• BigNumber as contract methods param? (TxBuilderHelper.getMinimumNameFee) #1251
• (wip) Replace http compiler calls with calldata en/decode lib for contract calls #1259

we should maybe also consult with @dincho here.

[marc0olo]

we should make a proposal how to proceed here.

[marc0olo]

here the calldata-lib implementation:

• https://github.com/aeternity/aepp-calldata-js

one important note here:

• we can change code in both repositories! ... we should decide how to proceed with each component (SDK and calldata-lib)
• we don't have to adapt everything in one repo of course ;-)

[marc0olo]

another library related to that which is included in the SDK right now:

• https://github.com/aeternity/json-bigint

[davidyuk]

Some time before I was investigating the ability to implement a custom wrapper around bigint to represent ae coints, but this feature on TS side is missed microsoft/TypeScript#2361

[davidyuk]

Approximate roadmap (each step may be done separately):

• don't use strings as numbers
• use BigInt instead of BigNumber (drop BigNumber completely)
• implement Ae wrapper around BigInt (uncertain)

I've touched on this topic in #1762 but it is too heavy for sdk@13