Fix AccountResponse and requests

[fracek]

I think this fixes #157 (I had the same issue). I also finished converting requests to use string instead of KeyPair.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #158 into master will increase coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #158      +/-   ##
==========================================
+ Coverage   85.71%   85.82%   +0.11%     
==========================================
  Files         211      211              
  Lines       11442    11443       +1     
==========================================
+ Hits         9807     9821      +14     
+ Misses       1635     1622      -13

Impacted Files	Coverage Δ
stellar-dotnet-sdk/responses/AccountResponse.cs	90.32% <100%> (+41.93%)	⬆️
...lar-dotnet-sdk/requests/FriendBotRequestBuilder.cs	100% <100%> (ø)	⬆️
...tellar-dotnet-sdk/requests/TradesRequestBuilder.cs	87.87% <100%> (+0.37%)	⬆️
...llar-dotnet-sdk/requests/AccountsRequestBuilder.cs	100% <100%> (ø)	⬆️

---

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 7837367...9290fcf. Read the comment docs.

[elucidsoft]

One thing of note on this, this actually was a breaking change since we changed the signature from KeyPair to string, which means this should have been deployed under a major. I missed this and already merged it. Luckily we just deployed a major revision so this hopefully won't impact many.

[fracek]

You are right, sorry I missed that!