feat: add slot and logic for forgetting pin code

[aelf-lxy]

add slot and logic for forgetting pin code, close #170

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.76%. Comparing base (7196729) to head (2ed50f8).
Report is 14 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #172   +/-   ##
=======================================
  Coverage   89.76%   89.76%           
=======================================
  Files          21       21           
  Lines         215      215           
  Branches       70       70           
=======================================
  Hits          193      193           
  Misses          8        8           
  Partials       14       14           

Flag	Coverage Δ
unittests	89.76% <ø> (ø)

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