Fix transaction card and gas calculations

[pelle]

• [x] Respect gas passed into the request
• [x] Respect gasPrice passed into the request
• [x] Correctly handle errors in estimateGas
• [x] Move gas estimation code into separate forked process which should make cards faster
• [x] Don't store BN's in state, use float and string
• [x] Move all gas calculations into backend and not in UX
• [x] Always show value if available (it was hidden under advanced tab)

[codecov[bot]]

Codecov Report

Merging #158 into develop will increase coverage by 0.3%. The diff coverage is 77.14%.

@@            Coverage Diff             @@
##           develop     #158     +/-   ##
==========================================
+ Coverage    55.36%   55.67%   +0.3%     
==========================================
  Files          254      255      +1     
  Lines         8540     8552     +12     
  Branches      1722     1714      -8     
==========================================
+ Hits          4728     4761     +33     
+ Misses        3402     3381     -21     
  Partials       410      410

Impacted Files	Coverage Δ
lib/components/shared/Button.js	92.3% <ø> (ø)	:arrow_up:
lib/sagas/startupSaga.js	0% <ø> (ø)	:arrow_up:
lib/sagas/blockchain.js	4.41% <0%> (+0.02%)	:arrow_up:
lib/components/newRequest/types/TransactionCard.js	54.48% <68.75%> (+11.03%)	:arrow_up:
lib/sagas/requests/transactionRequest.js	57.29% <87.75%> (+4.81%)	:arrow_up:
lib/navigators/navigation.ts	0% <0%> (ø)	:arrow_up:
lib/navigators/index.ts	0% <0%> (ø)	:arrow_up:
lib/utilities/requestQueue.js	0% <0%> (ø)
... and 1 more

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