personal_analysis_view: update state of AverageHours.

[Apollo1840]

• what is this feature about?
  as title

• suggested solution:
  calculate it in frontend
  or calculate it through backend

• potential affected files?
  frontend/src/components/personalanalysisview/PersonalAnalysisView.jsx
  backend/studytimeboard/routers.py

• are there some depending RP that is not approved yet?
  no