rpc: return bse64 bytes from getblock, getblockheader, getrawtx

[AnnaShaleva]

Close #1522

[codecov]

Codecov Report

Merging #1525 (6bb81d9) into master (bdd073a) will decrease coverage by 0.04%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master    #1525      +/-   ##
==========================================
- Coverage   77.60%   77.55%   -0.05%     
==========================================
  Files         229      229              
  Lines       17942    17933       -9     
==========================================
- Hits        13923    13908      -15     
- Misses       3049     3052       +3     
- Partials      970      973       +3     

Impacted Files	Coverage Δ
pkg/rpc/server/server.go	78.03% <66.66%> (ø)
pkg/rpc/client/rpc.go	83.64% <100.00%> (-2.29%)	⬇️

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