Fix clippy errors/warnings when upgrading to Rust 1.51

[thanethomson]

Rust's 1.51 release brought with it a number of new clippy errors and warnings. This PR attempts to address the bulk of them.

Unfortunately this results in some breaking changes to data structures' names, because they were improperly named up to now according to Rust's API guidelines.

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Updated CHANGELOG.md

[codecov-io]

Codecov Report

Merging #839 (94fbd01) into master (8f29824) will decrease coverage by 26.3%.
The diff coverage is 18.6%.

@@            Coverage Diff            @@
##           master    #839      +/-   ##
=========================================
- Coverage    55.7%   29.3%   -26.4%     
=========================================
  Files         198     194       -4     
  Lines       14063   10766    -3297     
  Branches     3692    4444     +752     
=========================================
- Hits         7834    3156    -4678     
+ Misses       5897    4652    -1245     
- Partials      332    2958    +2626     

Impacted Files	Coverage Δ
abci/src/error.rs	0.0% <0.0%> (ø)
light-client-js/src/utils.rs	0.0% <0.0%> (ø)
light-client/src/components/verifier.rs	62.8% <0.0%> (-28.4%)	⬇️
light-client/src/lib.rs	100.0% <ø> (ø)
light-client/src/operations/commit_validator.rs	93.9% <0.0%> (-6.1%)	⬇️
light-client/src/operations/voting_power.rs	48.0% <0.0%> (-40.6%)	⬇️
light-client/src/predicates/errors.rs	28.5% <0.0%> (-26.2%)	⬇️
light-client/src/store/sled.rs	36.9% <ø> (-32.2%)	⬇️
light-client/src/supervisor.rs	31.5% <0.0%> (-48.7%)	⬇️
light-node/src/commands/start.rs	0.0% <0.0%> (ø)
... and 210 more

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