Refactor LocalStorage API

[SebastienGllmt]

The current LocalStorageApi causes a lot of code duplication if we add more settings (which we plan to)

code here

There should instead be a type-parameterized class that takes a default value as an argument that we reuse for these settings.

Hopefully this refactoring would also allow us to add // @flow to the file to enable type-checking

[SebastienGllmt]

Note: related to #71

[jarstorm]

Hello, and thank you for your contribution.
We're currently reviewing long-standing issues to keep the tracker manageable. As this issue hasn't seen activity in some time, we're closing it.
If the problem persists or you'd like to follow up, feel free to comment and we'll reopen it.