Use new issue form

[dukecat0]

Closes #801

New issue form has a friendlier look.

And I've set blank_issues_enabled to true in config.yml just in case someone will need to open a blank issue.

[bhrutledge]

@meowmeowmeowcat Thanks for taking the time to submit this. Once again, apologies for the delay, but this particular change is a lower priority for me, and I suspect there will be a decent amount of discussion. After a quick scan, I see a handful of copy-edits that I'd like to make, and I think there are a few ways to make it friendlier. I'll aim to push my suggestions "soon".

[bhrutledge]

Superseded by #1022