ITP Welcome week tweaks

Things generally went super well

A few things I'd suggest we change based on this week:
* We spent time in class making sure everyone was in the right Slack and everyone was in the right Slack channels. We should add this as an activity to the Welcome day-plan. Having done this should be in the sprint success criteria
* We should explain the expenses policy in the day-plan
* Some people didn't know they could use Slack on a computer (and it's much easier than on a phone) - we should signpost this
* We should remove the coursework planner centric steps from the "Next steps" day plan activity - they're part of the prep for next sprint, and confused people who thought they should already know/have-done them