Added Visual Studio 2015 .vs folder

Visual Studio 2015 moved all the user specific configuration to a .vs folder, which shouldn't be tracked.

UnrealEngine.gitignore

+# Visual Studio 2015 user specific files
+.vs/
+
 # Compiled Object files
 *.slo
 *.lo
@@ -57,3 +60,5 @@ Intermediate/*
 
 # Cache files for the editor to use
 DerivedDataCache/*
+
+