The setting manager doesn't support if new package remove settings

[ulybu]

some scenarios:

• in a newer version, the extension have one less setting. The sync'ed setting won't be deleted
• If we remove a setting and add another one (or rename one), it won't notice it and the new setting won't be added

[ulybu]

src/shared/config.js:40

var syncConfKeys = Object.keys(this.userConf)
  , defaultConfKeys = Object.keys(this.getDefault())
  ;

// @TODO Only test if there is new settings. Need to test if missing or replaced
if(syncConfKeys.length !== defaultConfKeys.length){ 
//extends sync with default