Converted codebase to typescript and background page/worker

[mocanew]

Fixes #108, #172

Using a background page/worker boosts perceived performance a lot compared to the current way of interacting with sync storage (all actions are now instant).

Improved perceived extension load speed when first opening YouTube: buttons are added as soon as possible rather than checking for page elements.

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The extension now needs two zip files, one for firefox and one for chrome, due to manifest v2 and v3 incompatibilities (background script vs service worker - firefox doesn't yet support service workers).

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[mocanew]

@OsaSoft this PR is ready, have a look at it when you have some free time.

[tummyslyunopened]

@OsaSoft @mocanew Is the plan still to convert to TS / implement these changes. I have been using this extension a lot recently and have contributions ready for a few issues, but would like to know if this is welcome / should new contributers wait until TS is adopted?