Use styled-components in Loader

[adityagarg06]

Progress on #1760

Changes:

• Migrate styles from _loader.scss into individual styled components in the Loader.jsx file.
• Deleted the _loader.scss.

Looks identical to before on Windows Chrome.

I have verified that this pull request:

• [x] has no linting errors (npm run lint)
• [x] has no test errors (npm run test)
• [x] is from a uniquely-named feature branch and is up to date with the develop branch.
• [x] is descriptively named and links to an issue number, i.e. Fixes #123