core: allow to invoke verify of native contracts

[fyrchik]

Related neo-project/neo#1995 .

[codecov]

Codecov Report

Merging #1476 into master will increase coverage by 0.01%.
The diff coverage is 84.61%.

@@            Coverage Diff             @@
##           master    #1476      +/-   ##
==========================================
+ Coverage   77.40%   77.42%   +0.01%     
==========================================
  Files         227      227              
  Lines       17660    17671      +11     
==========================================
+ Hits        13669    13681      +12     
+ Misses       3050     3049       -1     
  Partials      941      941              

Impacted Files	Coverage Δ
pkg/core/blockchain.go	73.89% <84.61%> (+0.10%)	⬆️
pkg/core/native/oracle.go	73.01% <0.00%> (+0.52%)	⬆️
pkg/network/metrics/metrics.go	81.81% <0.00%> (+18.18%)	⬆️

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[roman-khimov]

@fyrchik --- please update it a little according to neo-project/neo#1998.

[roman-khimov]

ping