Added Border Radius

[Anubhav-Vashishtha]

Fixes #2909

Changes:

I have verified that this pull request:

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

[raclim]

Thanks for your work on this! I think I don't feel completely set on implementing this since I'm not sure if it's consistent with the design of the rest of the editor (also outlined in #2909 (comment)). I'm going to close this for now, but please feel free to work on other issues!