Basic Stake testing

Refers to #157 (closed)

• Adds staking test
• Tidies up test fixture structure
• Ensures that test fails when external calls are attempted that are not handled explicitly in the test

@gitkai @jpthor I would love it if you could just check that the touch points of where I am testing are correct:

STAKE:

https://gitlab.com/thorchain/bepswap/bepswap-react-app/blob/ab06b3e84c331a9c297c0ca0aad2f7864e848395/cypress/integration/stake.spec.js

SWAP:

https://gitlab.com/thorchain/bepswap/bepswap-react-app/blob/ab06b3e84c331a9c297c0ca0aad2f7864e848395/cypress/integration/swap.spec.js

These are not meant to be comprehensive at all but it would be good to check that they are testing the right things for the simple cases they present here.

It would be good to check the mocks are reasonable too - I just copied them from live API calls.

Just after a sanity check as I don't have heaps of business domain background.