Localstorage key scoped to prefix

[NicoZelaya]

JS SDK

What did you accomplish?

• Scoped my segments data in localstorage inside the same prefix than the other keys.

How do we test the changes introduced in this PR?

• Run the unit tests
• Validate running on a web, you can introduce a few old keys from the console. Reach out to me if you want some example sentences.

Extra Notes

• The goal is to make the change without leaving old cache keys behind.

[EmilianoSanchez]

LGTM