refactor: handle response as string and build transactions with BigNumber

[luciorubeens]

Core 2.5 modified the values for string instead of numbers.

Resolves #1310

What kind of change does this PR introduce?

• Bugfix
• Feature
• Refactor
• Performance
• Tests
• Build
• Documentation
• Code style update
• Continuous Integration
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

Does this PR release a new version?

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the develop branch, not the master branch
• All tests are passing
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

[codecov-io]

Codecov Report

Merging #1317 into develop will increase coverage by 0.37%.
The diff coverage is 69.38%.

@@             Coverage Diff             @@
##           develop    #1317      +/-   ##
===========================================
+ Coverage    39.84%   40.22%   +0.37%     
===========================================
  Files          229      231       +2     
  Lines         6354     6381      +27     
  Branches      1256     1256              
===========================================
+ Hits          2532     2567      +35     
- Misses        3600     3606       +6     
+ Partials       222      208      -14

Impacted Files	Coverage Δ
...nsaction/TransactionConfirm/TransactionConfirm.vue	28.57% <ø> (ø)	⬆️
...ransaction/TransactionForm/TransactionFormVote.vue	12.22% <ø> (ø)	⬆️
...action/TransactionForm/TransactionFormTransfer.vue	8.13% <ø> (-0.07%)	⬇️
src/renderer/models/profile.js	100% <ø> (+100%)	⬆️
...ponents/Wallet/WalletHeading/WalletHeadingInfo.vue	63.15% <ø> (+0.99%)	⬆️
src/renderer/models/peer.js	100% <ø> (ø)	⬆️
src/renderer/pages/Profile/ProfileAll.vue	77.14% <ø> (+0.67%)	⬆️
src/renderer/models/transaction.js	0% <0%> (ø)	⬆️
src/renderer/store/modules/profile.js	58.82% <100%> (ø)	⬆️
src/renderer/models/base.js	95% <100%> (+0.26%)	⬆️
... and 18 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4a64520...fce4a09. Read the comment docs.

[dated]

Presumably closes #1310 ;)

[luciorubeens]

@dated Yes, thanks!