add dialog for closing booking year to allow selection of carry forward account

[lg2de]

Fixes #11

[codecov-io]

Codecov Report

Merging #27 into master will increase coverage by 0.05%.
The diff coverage is 86.84%.

@@            Coverage Diff             @@
##           master      #27      +/-   ##
==========================================
+ Coverage   86.28%   86.34%   +0.05%     
==========================================
  Files          29       31       +2     
  Lines        2574     2592      +18     
  Branches      338      339       +1     
==========================================
+ Hits         2221     2238      +17     
  Misses        286      286              
- Partials       67       68       +1     

Impacted Files	Coverage Δ
...rc/SimpleAccounting/Presentation/ShellViewModel.cs	83.19% <76.47%> (-0.07%)	⬇️
...impleAccounting/Presentation/CloseYearViewModel.cs	93.75% <93.75%> (ø)
...ccounting/Presentation/CloseYearDesignViewModel.cs	100.00% <100.00%> (ø)

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