feat: repurpose as open edx footer

[abutterworth]

Simplify the prop api in preparation for making a second, Open edX footer, that is swappable. Most edX values are now baked in.

---

Usage

To install frontend-component-footer into your project

   npm i --save @edx/frontend-component-footer

Component Usage

   import Footer from '@edx/frontend-component-footer';
   import footerMessages from '@edx/frontend-component-footer/src/i18n/index';

   ...

   <Footer
      handleAllTrackEvents={(eventName, properties) => {/* track click event */}}
      onLanguageSelected={(languageCode) => {/* set language */}}
      supportedLanguages={[
         { label: 'English', value: 'en'},
         { label: 'Español', value: 'es' },
      ]}
   />

• handleAllTrackEvents (required)
• onLanguageSelected (optional)
• supportedLanguages (optional)

Requirements

This component uses @edx/frontend-i18n. Any containing app must provide @edx/frontend-i18n as a peer dependency, and be wrapped inside an IntlProvider element, whether or not your consuming application is actually localized. For a basic default locale (English) version, follow the IntlProvider example in the sample application in src/index.jsx <src/index.jsx>__.

[matthugs]

Took a look-see and think we could use more eyes than just mine, but this looks good