Introduce conflict resolution to Issues webhook

[begedin]

Problem

There can be cases where the issue webhook data is not the most recent data we have. For example, github could go down, someone might post on codecorp, etc.

In those cases, we should introduce conflict resolution. The most basic approach would be to compare the timestamps on the github payload and our own record and have the most recent data win.

[joshsmith]

I'm not sure if this is still relevant or not. Are you clear on this @begedin?

[begedin]

#878 might be part of this, but I'm still not sure how the behavior will work or if we need to deal with this at this point.