Update DataServiceImpl.java
Merge pull request #165 from khfayzullaev/patch-1

Fix updateDevice method
Update DataServiceImpl.java

Solves Problem #166 `merge()` erases the *Latest Position* field. That is why, Markers are disappearing. We have to upgrade the Device Details keeping that very field.
Merge pull request #167 from khfayzullaev/patch-1

Fix missing markers on update
Fix code formatting
Update GWT library
Use CDN for OpenLayers (fix #150)
Update GXT to 3.1.0 beta
Merged with upstream. Updated GWT to 2.6.0, GXT to 3.1.0-beta. Incremented version to 2.8-SNAPSHOT