Add support for plugins

We should try and modularize the code base so the jquery/ajax and window.onerror logic is separated out. So if you're not using it, you're not paying the overhead cost.

Start by locating the jquery/ajax and window.onerror integrations in the JavaScript codebase and read how they are initialized. Done means those integrations can be separated as optional plugins so users who do not use them avoid their overhead; the issue provides no named tests or files.

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