Improve diagnostics for package initialization errors

[jasonrudolph]

To aid in diagnosing and debugging package initialization errors (#266), this pull request incorporates the changes from atom/teletype-client#50 to provide a pre-filled GitHub Issue body with useful diagnostic information.

For example, clicking on the atom/teletype link in the popover...

...will prefill an issue like this:

Verification Process

• Simulate a failed request by turning off wi-fi
• Simulate a failed response by hacking the local teletype-server to return a non-JSON response
• Ensure that pointing to the production server still allows successful collaboration in a portal

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🍐'd with @as-cii

[50Wliu]

Wording suggestion: visit atom/teletype and open an issue sounds to me like I have to click the link, and then create an issue by myself. However, what's really happening now is that link creates the issue contents for me and all I have to do is press the big green button. So my suggestion is to incorporate that aspect into the text, like If the problem persists, please [open an issue](link_goes_here) (which I think still doesn't convey the fact that you'll have an issue prefilled for you, but I can't think of anything better).

💭?

[jasonrudolph]

Wording suggestion

@50Wliu: Thanks for caring about this and thanks for the suggestion. If you're interested in opening a pull request to update the wording, I'll happily review it for you.