[WIP] Set up Google analytics

[obulat]

Fixes #62 and #64

Description

Set up Google analytics for chooser. The following events are tracked:

• User opening the page

• User clicking on any of the 'Help' button
  Information sent: HelpSection.clicked.<button-title>

• User opening Attribution Details step, when we can assume that the user has selected a license :
  Information sent: Stepper.licenseSelected.<short name of selected license>

• User selecting a license from the dropdown
  Information sent: LicenseDropdown.licenseSelected.<short name of selected license>

• User copying attribution details
  Information sent:
  Attribution.copied.<Stringified JSON: license: short name of selected license, codeType: one of html/rich-text, fieldsFilled: <fieldName: true/false>>

Checklist:

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the master branch of the repository.
• My commit messages follow best practices.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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[akmadian]

Apologies for not getting to this sooner. Looks great so far! Some little things here and there, though

[akmadian]

Also, please add #64 to the "Fixes" line in your PR body

[akmadian]

Looks great! Go ahead and merge whenever :)

[obulat]

Thank you, Ari, your changes made it much better :)