Modified course management code in common.js

- rewritten guessCapImgName so that it computes a rounded angle that
correspond to an image name (e.g. 0.png), with 8 sectors for the moment
(but extensible to much more easily)
- moved course images to /ressources/img/map-courses
Modified POI

- removed useless POI
- modified data for POIT "iut"
Simplified guessCapImgName and guessSpeedIconName  functions

- removed useless call to Math.abs in guessCapImgName
- removed duplicate test in guessSpeedIconName
Modified speed thresholds in map-online