Fix: Inconsistency in statistics summaries

[GitOldGrumpy]

Fix issue: #281

• Fix for double addition for first item in a year
• Fix for only single month being returned in a year summary
• Fix for no data being returned. This happens when there has no been "driving" days in the date range requested.

[codecov]

Codecov Report

Attention: 15 lines in your changes are missing coverage. Please review.

Comparison is base (9895806) 72.47% compared to head (9e52bba) 72.36%.
Report is 3 commits behind head on master.

Files	Patch %	Lines
mytoyota/models/vehicle.py	0.00%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #282      +/-   ##
==========================================
- Coverage   72.47%   72.36%   -0.11%     
==========================================
  Files          28       28              
  Lines        1355     1357       +2     
==========================================
  Hits          982      982              
- Misses        373      375       +2     

Flag	Coverage Δ
unittests	72.36% <0.00%> (-0.11%)	⬇️

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[CM000n]

Looks good 🎉