Merge pull request #57 from Kloadut/master

[fix] Drastically increase the speed of first synchronization + fix dele...
Merge pull request #59 from Kloadut/master

Backport of chokidar + wording and fixes
[fix] Do not launch synchronization in 'live' mode + wording (fixes #61)
[enh] Copy DB documents manually at the first sync (like cozy-mobile)
[fix] Do not put chokidar.js in the backend directory
[ref] Big refactoring part1 (WIP)