Fix/12 and references

[hoani]

This PR addresses #12 and also updates the @polkadot/ references to 1.8.1 for compatibility with the latest pl^g node.

The PR steals changes from #13, making the fix/12 branch redundant.

Tested and works with current pl^g, but throws some warnings (in the api-template project):

hoani@Hoani-MBP api-template % node index.js
Connecting to ws://localhost:9944
2020-06-22 14:42:40        API/INIT: RPC methods not decorated: genericAsset_registeredAssets, state_queryStorageAt}
Unable to resolve type AssetInfo, it will fail on constrution
Unknown signed extensions [OptionSignedExtension] found, treating them as no-efect
Unknown signed extensions [OptionSignedExtension] found, treating them as no-efect
Unknown types found, no types for AssetInfo,schnorrkel::Randomness,schnorrkel::RawVRFOutput
Unknown signed extensions [OptionSignedExtension] found, treating them as no-efect
Unknown signed extensions [OptionSignedExtension] found, treating them as no-efect
You are connected to chain Development using Plug Node v2.0.0-alpha.5
Alice's balance: 999999987984347752053
Bob's balance: 1000000000000000049503
Alice is transferring 12345 to Bob
Transaction submitted with hash 0xda3fd2e018867aa7d9f262e777a9d8e34d9cf66566f46d291b23fa7920b3527f

Changes

• Brought in changes from fix/12 so that we can submit extrinsics again
• Updated references to @polkadot libs so that it works with 1.8.1 which is compatible with latest plug.

Concerns

• Raised an issue ticket to address warnings

[jordy25519]

lgtm! for others landing here CI is broken because plug image isn't being published properly at the time of writing