Note: It is necessary to have no indentation otherwise spaces are interpreted.

See discussion of options: https://github.com/paritytech/fether/pull/307#discussion_r244695598

* Remove `isEstimatedTxFee` since can just use `estimatedTxFee` to achieve same functionality

* Rename `newEstimatedTxFee` to `newGasEstimate` since it returns a value that's used for the `values.gas` prop

* Update `estimatedTxFee` to return `null` if the amount, gas, gasPrice values provided aren't valid, instead of returning the calculated estimated tx fee

* Wrap call to `estimateGas` in a try/catch block that throws error "Unable to estimate gas" when error thrown when calling `estimateGas` in TxForm.js

* Move check `if (!ethBalance) {` earlier in function

feat: Relates to #311. Switch to Blockscout. Update tx link

* Create TxDetails component and move relevant instance methods from TxForm into TxDetails

* Fix linting warning `Using target="_blank" without rel="noopener noreferrer" is a security risk: see https://mathiasbynens.github.io/rel-noopener`

* Remove isCancelled

* Remove estimatedTxFee from state

* Sort instance methods into alphabetical order

* Refactor by adding isEstimatedTxFee to check gas properties defined on form values

* Add instance method estimatedTxFee to return calculation based on gas values

* Move functions out of render function and change them into instance methods

* Remove duplicate check for whether values.gas existed

* Fixes error `Uncaught TypeError: Cannot read property 'resolve' of null at flush` that is generated after both valid amount and recipient values are entered

Update @parity/* packages & fix #298

Add Max button to send the whole balance