[Docs] Refactor for new class based approach

[SeanNaren]

I have a few off cycles to try to get the documentation up to date. Related #223

Missing pieces

• [x] Update quickstart guide
• [x] Remove Optimizations (except SparseML, Link to Lightning docs in quickstart)

[codecov[bot]]

Codecov Report

Merging #243 (86d8a16) into master (ff4f3e8) will increase coverage by 0%. The diff coverage is 78%.

@@          Coverage Diff          @@
##           master   #243   +/-   ##
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  Coverage      74%    74%           
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  Files          73     73           
  Lines        1568   1576    +8     
=====================================
+ Hits         1163   1169    +6     
- Misses        405    407    +2