Restructure crypto code

[0x009922]

Currently:

• @iroha2/client contains a crypto singleton, which should be set by users with setCrypto function before using related client functions
• Each crypto target library (@iroha2/crypto-target-*) exports the same crypto wrap around an actual WASM, a JS layer.
• @iroha2/crypto-core exports types which are guaranteed to match with crypto's from targets.
• This is backed by a complex Rollup + TypeScript configuration

Proposal:

• Move crypto singleton to @iroha2/crypto-core
• Remove wraps generation for each target. Each target only re-exports raw WASM API as crypto, which is guaranteed to be the same between all the targets.
• Define the convenient JS layer around raw WASM API once in @iroha2/crypto-core. Make this layer rely on the raw crypto singleton.

Outcomes:

• Simpler and clearer way of using @iroha2/crypto-*
• Simpler build configuration

[0x009922]

Oh, I created almost the same issue before...

• Move WASM singleton from @iroha2/client to @iroha2/crypto-core #164

[0x009922]

But it was actually not the same. This issue also points out that "interface wrap" could be removed to reduce repetition.

[0x009922]

Closed by #199