Bug 939174 - Launch whats new FTU tutorial to demo edge gestures etc.

* Add shared VersionHelper
* Unit tests for VersionHelper, FTULauncher
* Check and set device.previous_os in FTULauncher/FTU app
* Launch full ftu when ftu.enabled always
* Launch 'whats new' ftu tutorial when upgrade detected
* Add config for 1.3-2.0 and 1.4-2.0 upgrade tutorial
This is in both scenarios, so we could move out of the IF/ELSE in the top of it:
`if (!AppManager.isInitialized) {`
 `AppManager.init();`
`}`

`if (versionInfo.isUpgrade()) { ...`