Return responsibility of mcl/wasm-mcl usage to HubbleProject

[jzaki]

HubbleProject takes responsibility for a single initialisation of mcl (thus wasm-mcl) with its BLSSignerFactory singleton.
bls-wallet-signer bypasses this and creates BLSSigners directly and assumes repeated calls to the wasm-mcl init function will always be okay, (code-smell: "inapprorpiate intimacy").
To maintain separation of concerns, use of mcl/wasm-mcl should remain contained within HubbleProject unless really needed.

Related: "Object Orgy" regarding private key access in BLSWallet, mentioned here