Fix display of validation errors

[daniel-thom]

This resolves https://github.com/NREL-SIIP/PowerSystems.jl/issues/748.

I also added some minor improvements elsewhere.

[codecov[bot]]

Codecov Report

Merging #238 (28d329e) into master (5ba88bc) will decrease coverage by 0.03%. The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #238      +/-   ##
==========================================
- Coverage   75.37%   75.33%   -0.04%     
==========================================
  Files          43       43              
  Lines        3123     3122       -1     
==========================================
- Hits         2354     2352       -2     
- Misses        769      770       +1     

Flag	Coverage Δ
unittests	75.33% <33.33%> (-0.04%)	:arrow_down:

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

Impacted Files	Coverage Δ
src/validation.jl	11.32% <0.00%> (ø)
src/utils/logging.jl	89.78% <100.00%> (ø)
src/utils/utils.jl	61.18% <0.00%> (-0.43%)	:arrow_down:
src/utils/lazy_dict_from_iterator.jl	96.15% <0.00%> (-0.15%)	:arrow_down: