feat(eth): support transferring ERC20 tokens

[faustbrian]

Resolves #232

[codecov]

Codecov Report

Merging #234 into master will decrease coverage by 0.38%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #234      +/-   ##
==========================================
- Coverage   83.20%   82.82%   -0.39%     
==========================================
  Files          26       26              
  Lines         774      780       +6     
  Branches      102      103       +1     
==========================================
+ Hits          644      646       +2     
- Misses        127      131       +4     
  Partials        3        3              

Impacted Files	Coverage Δ
src/services/transaction.ts	58.86% <0.00%> (-1.14%)	⬇️
src/services/fee.ts	94.11% <0.00%> (ø)

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