Task/script refactor (#446)

* scripting working with race conditions

* new service works with no race conditions

* use new scripting service and commented out tests

* refactored peek definition to use mssql-scripter

* fixed peek definition tests

* removed auto gen comment

* fixed peek definition highlighting bug

* made scripting async and fixed event handlers

* fixed tests (without cancel and plan notifs)

* removed dead code

* added nuget package

* CR comments + select script service implementation

* minor fixes and added test

* CR comments and script select

* added unit tests

* code review comments and cleanup

src/Microsoft.SqlTools.ServiceLayer/Workspace/Workspace.cs

@@ -137,7 +137,7 @@ namespace Microsoft.SqlTools.ServiceLayer.Workspace
                     // any extraneous slashes
                     Uri fileUri = new Uri(filePath);
                     filePath = fileUri.LocalPath;
-                    if (filePath.StartsWith("//") || filePath.StartsWith("\\\\")) 
+                    if (filePath.StartsWith("//") || filePath.StartsWith("\\\\") || filePath.StartsWith("/")) 
                     {
                         filePath = filePath.Substring(1);
                     }