Assignement page & backend skeleton ready

It just need the assignement code and logic now...
Automatic assignement working

- Misc. updates:
    - models.Assignement.{MANUAL, AUTOMATIC}
    - domain.assignement.Stats() for convenience
    - misc. small fixes
- Fully working assignement algorithm
    - tries to match from Activite that need the most help (lowest
      places filled ratio)
    - find available Volontaire who work the least, have the best gender
      and can make it in time
    - 30 min per transport, no matter the distance -> room for
      improvement
Fix activite priority in assignement (int. div. pb)

Euclidian division -> float division
Hard constraint of time worked
Assignement: fix login params error

swapped 2 ints
Travel time: memoization, known values