MemoryAccount types, fix example aepp

[davidyuk]

This PR is supported by the Æternity Foundation

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 79.80%. Comparing base (a21bc1f) to head (bdcd888).
Report is 1 commits behind head on develop.

Files	Patch %	Lines
src/account/Memory.ts	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1955      +/-   ##
===========================================
- Coverage    79.91%   79.80%   -0.11%     
===========================================
  Files          101      101              
  Lines         3450     3452       +2     
  Branches       733      734       +1     
===========================================
- Hits          2757     2755       -2     
- Misses         381      384       +3     
- Partials       312      313       +1     

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