Support a configuration file

[antross]

Probably just JSON to begin with, but ideally sitting somewhere that one config file can be used across all browsers. Will need to double-check if browser extensions can read files from disk, but if not a JSON sitting in the /dist folder could work for now (though that might require reloading the extension after changes).

Initial thoughts on configurable items:

• customize max trace length
• support for excluding APIs (or categories of APIs) from the trace
• triggers for automatically starting/stopping tracing (specific API calls or events)
• filters to capture only specific frames (e.g. by URL)