when a new issue is reported & has a test, automatically test it

[ckerr]

When a new issue is reported, even if it's not a regression (e.g. even if no "last known working version" was filled out), bugbot should see if it can confirm the issue and report back in a comment + labels.

The full implementation is still up for debate but some pieces are clear:

• Update labels as necessary so that bugbot can correctly handle future updates to the issue
• Make clear whose responsibility the next step is: a maintainer or the OP?
• Give that person the info they need to make the next step

All cases:

1. MUST set a label reflecting the bugbot state of the bug. Bugbot needs this to correctly determine the issue's state the next time there is an update in the issue.
2. MUST report back in the bugbot issue comment the test results. Related Fiddle discussion @ feat: command-line option to run test on matrix of Electron versions fiddle#672

if the test failed

1. (brainstorming) MAY set other labels e.g. a 'confirmed'
2. (brainstorming) MAY set platform labels depending on which or all platforms the test passed or failed on
3. (brainstorming) MAY set version numbers depending on branches affected by the bug

If the test passed:

2. (brainstorming) MAY notify OP via an @ in the comment
3. (brainstorming) MAY mark the issue as blocked pending a gist revision

If the test failed to run:

2. (brainstorming) MAY notify a maintainer @ in comments
3. (brainstorming) MAY notify a maintainer in Slack
4. (brainstorming) MAY include collapsed text of the fiddle output in bugbot's issue comment
5. (brainstorming) MAY have a link to a cloud CI output of the failed run