Add ParentalSettings to LoggedOnCallback

[JustArchi]

I've verified that this works properly, and it's a big help for those apps that want/need to interpret those settings, for example in order to determine if ParentalSettings.is_enabled.

I could expose resp.parental_settings alone and expect from the consumer to do the deserialization himself, but I believe that we can aid him a little since there is nothing else he should be doing with that data anyway. Let me know if there is anything you'd change in this implementation.

Thank you in advance for considering this PR.

[codecov-io]

Codecov Report

Merging #707 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #707      +/-   ##
==========================================
- Coverage   24.38%   24.36%   -0.03%     
==========================================
  Files          89       89              
  Lines        8800     8808       +8     
  Branches      742      743       +1     
==========================================
  Hits         2146     2146              
- Misses       6522     6530       +8     
  Partials      132      132

Impacted Files	Coverage Δ
...t2/SteamKit2/Steam/Handlers/SteamUser/Callbacks.cs	2.89% <0%> (-0.15%)	⬇️

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