Having to "Enable Sourcegraph on this site" is very non-obvious, makes it hard to rollout to multiple users

Created by: slimsag

When installing the Sourcegraph Chrome extension, you have to right click and Enable Sourcegraph on this site. This has multiple problems which are a major hurdle to making use of and rolling out the Chrome extension:

1. It is not a part of our on-boarding flow for the Chrome extension, which makes it extremely non-obvious. For example, clicking the Sourcegraph toolbar icon shows Connected -- "but the extension doesn't work on my code host!"
2. We can roll out the Chrome extension to an entire organization via Google Apps, but users will still have to Enable Sourcegraph on this site. Our onboarding flow should take this into consideration as well.