review-fix: Tweak tx details. Convert functions into instance methods.

* 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