rpc: add NEP11 and NNS interfaces to RPC Client

[AnnaShaleva]

Close #1836

[codecov]

Codecov Report

Merging #1857 (ffc2ad3) into master (44c87a4) will decrease coverage by 0.11%.
The diff coverage is 56.34%.

@@            Coverage Diff             @@
##           master    #1857      +/-   ##
==========================================
- Coverage   83.31%   83.20%   -0.12%     
==========================================
  Files         283      286       +3     
  Lines       22467    22581     +114     
==========================================
+ Hits        18719    18788      +69     
- Misses       2592     2622      +30     
- Partials     1156     1171      +15     

Impacted Files	Coverage Δ
pkg/rpc/client/policy.go	60.00% <ø> (ø)
pkg/rpc/client/nep.go	43.24% <43.24%> (ø)
pkg/rpc/client/nep11.go	50.79% <50.79%> (ø)
pkg/rpc/client/nep17.go	52.63% <55.55%> (+3.05%)	⬆️
pkg/rpc/client/helper.go	60.00% <60.00%> (ø)
pkg/rpc/client/native.go	61.29% <63.63%> (+1.29%)	⬆️
pkg/core/native/name_service.go	82.18% <100.00%> (ø)
pkg/vm/emit/emit.go	100.00% <100.00%> (ø)
... and 4 more

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