Update link icon in text editor, Make external link open in new tab

[IshavSohal]

Related Item(s)

#384

Changes

• Updated the link icon for the "Insert Link" dropdown of the text editor
• Made hyperlinks created using "Add External Link (New Tab)" option of the dropdown open in a new tab

Notes

• The text editor, vue-markdown-editor, seems to use unicode characters for its icons. Initially, the link icon was e6fe. I've now switched it to 1f517.
• Before:
  
• After:
  

Testing

Steps:

1. Open an existing product (or create a new one)
2. Create a new text slide
3. Observe the new link icon
4. Open the "Insert Link" dropdown and click the "Add External Link (New Tab)" option
5. Enter https://www.google.com/ as the hyperlink
6. Save the product and open the preview
7. Scroll down to the last slide and click the link you created. It should open in a new tab.

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This change is 

[github-actions]

Your demo site is ready! 🚀 Visit it here: https://ramp4-pcar4.github.io/storylines-editor/issue-384-fix

[RyanCoulsonCA]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @IshavSohal)

[yileifeng]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @IshavSohal)