Prioritize Slack display name over username

[ImShyMike]

I've seen about 3 diferent people saying something like "why is my hackatime username my email now" as Hackatime was now using their slack username (the name field in the api), which defaults to the name part on their email.

This change makes the priority be:

display_name_normalized -> real_name_normalized -> name

Instead of the previous:

name -> real_name_normalized -> display_name_normalized