Require just one secret seal for the transfer method

[dr-orlovsky]

Closes #262

Requires RGB-WG/rgb#240

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 4 lines in your changes missing coverage. Please review.

Project coverage is 19.4%. Comparing base (070bfcd) to head (526c266).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/persistence/stock.rs	42.9%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #265     +/-   ##
========================================
- Coverage    19.4%   19.4%   -0.0%     
========================================
  Files          39      39             
  Lines        8610    8607      -3     
========================================
- Hits         1672    1671      -1     
+ Misses       6938    6936      -2     

Flag	Coverage Δ
rust	19.4% <42.9%> (-<0.1%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[zoedberg]

ACK 526c266