Add Prettier with tslint plugin and precommit hook

[agubler]

Type: feature

The following has been addressed in the PR:

• [x] There is a related issue
• [x] All code matches the style guide
• [ ] Unit or Functional tests are included in the PR

Description:

Adds support for Prettier to for code style rules and formatting. Include precommit hook that runs prettier on all .ts files and an npm script that runs prettier against the codebase.

Related to https://github.com/dojo/meta/issues/206

[codecov[bot]]

Codecov Report

Merging #21 into master will increase coverage by 0.36%. The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master      #21      +/-   ##
==========================================
+ Coverage   92.85%   93.22%   +0.36%     
==========================================
  Files           2        2              
  Lines          56       59       +3     
  Branches       13       15       +2     
==========================================
+ Hits           52       55       +3     
  Misses          2        2              
  Partials        2        2

Impacted Files	Coverage Δ
src/dijit/DijitWrapper.ts	94% <88.88%> (+0.38%)	:arrow_up:

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