Fix File Link Resolution

[dhoizner]

Fixes #1205, Fixes #1217, Fixes #1463

This pull changes the string replace to operate on the full quoted path passed to the loadThingies functions, which mitigates the issues that arise from having multiple files with the same name at different levels of the sketch hierarchy or a filename that is contained in the url of a different file.

Also updates installation.md to be more accurate with regards to S3_BUCKET_URL_BASE.

I have verified that this pull request:

• has no linting errors (npm run lint)
• is from a uniquely-named feature branch and has been rebased on top of the latest master. (If I was asked to make more changes, I have made sure to rebase onto master then too)
• is descriptively named and links to an issue number, i.e. Fixes #123

[catarak]

Thank you! I tested with the sketches linked in #1205 and #1463 and it is working great.

In the future, it would be helpful if you separated the changes into different PRs, since they are unrelated.