usability of gamification

Challenge
- [x] 'Reward as soon as every goal is reached' box checked by default
- [x] Clicking on a challenge kanban should open challenge view, not goal list
- [x] list of users readonly
- [x] start button on challenge

Badge
- [x] When creates a challenge from badge view, set by default badge to 'For Every Succeding User' field
- [x] List of badge on employee form not the first tab

Goals
- [x] better filter than "current"

Base
- [x] add field on `ir.model` to get inherited models and be able to retrieve the field list of inherits models as well
http://bit.ly/Zr4eET