ignore spam to scipost mail warnings

send message to slack channel on failure

refactor hcard

prevent college from previewing features

use annotated fellow queryset to defeat N+1 problem

fixes #346

reword assignment stage update email
disable automatic withdrawal after assignment deadline

fix refereeing reminders not being sent

fix appraisals count not showing
hide appraisal qualification count
prefer accepting offers of least overloaded fellow
skip deprecated test