Clean SendGrid Inbound Parse data

[gmittal]

Sometimes we get traces of past emails attached to email messages.

[gmittal]

Turns out that we're already using the standard library for inbound emailing parsing: https://github.com/github/email_reply_parser

I guess there are just some cases which can't be filtered out. Given that it's not a user-facing issue and it's only a volunteer thing, perhaps we could skip it?

cc: @ankitr

[ankitr]

hm… i think it's fine too move this off mvp but i think we shouldn't consider the volunteer experience lower priority than the user experience. let's still look at this once we're shipped.

[gmittal]

Seems as though the SendGrid npm module has changed significantly since Summer 2016 (latest version is 5.x and we're on 1.9.2). Seems as though they've added better support for Inbound Parse.

@johnguibas @xSmithereens: Can one of you experiment around with the new SendGrid npm module? It'll require some slight modifications to our copilot-communications package.

[gmittal]

This is a slight privacy issue because the unfiltered email may leak the user's signature, revealing sensitive information.