Add pre-commit linting hook

[bfreeds]

This commit closes #538 by adding a pre-commit hook that lints files staged for commits. This keeps the same eslinting rules as #555, but automates them in the developer process.

During the pre-commit hook, eslint --fix is run, which will automatically take care of formatting lint rules as per our config. I tried integrating prettier which does code formatting nicely, however ran into an issue where eslint --fix wouldn't automatically fix. I think it may be related to this issue: prettier/prettier-vscode#870, or have something to do with the complexity of using airbnb-base, ember, and prettier to work together.

Here's an example of how lint-staged and husky work in the git commit process, fixing some formatting:

And here's what this would do if you were trying to commit code with a lint error (which would also fail our ember tests):

[codecov]

Codecov Report

Merging #570 into develop will increase coverage by 0.92%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           develop    #570      +/-   ##
==========================================
+ Coverage    45.58%   46.5%   +0.92%     
==========================================
  Files          157     157              
  Lines         1516    1516              
==========================================
+ Hits           691     705      +14     
+ Misses         825     811      -14

Impacted Files	Coverage Δ
...mponents/project/project-area-selection-toggler.js	33.33% <0%> (+33.33%)	⬆️
...pp/components/project/project-area-selector-map.js	77.77% <0%> (+66.66%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f3e833d...661e4a9. Read the comment docs.