Initialize Sentry in development

[dcramer]

Couple of core reasons:

1. It ensures same behavior (code paths) for both prod and dev
2. It'll enable adoption of https://spotlightjs.com

[kentcdodds]

Very interesting! I remember seeing this at some point but never looked into it.

I'll need to play around with it before I decide to have it built into the template. If anyone wants to encourage me to play with it sooner, an example is the way to do that.