Change inbox cell iconography to show notification type

[rnystrom]

Move PR/Issue to smaller icon, more info gained from knowing if you’re mentioned or what not.

Bug Report Dump (Auto-generated)

Version 1.11.0 (1943)
Device: iPhone 7 Plus (iOS 11.0.1)
TestFlight: false

[rnystrom]

Nvm here. The reasons aren't what triggered the notification, only why you are getting the notification. Sort of an origin for your subscription. I saw "mention" and thought "you were mentioned" but it literally means you were mentioned in the thread. Kind of lame.

https://developer.github.com/v3/activity/notifications/#notification-reasons