Create MS.SqlTools.Credentials project (#249)

* Initial credential service files

* Clean-up hostloader

* Update build scripts to build credentials archive

* Move hosting files to new assembly

* Add credentials files to MS.SqlTools.Credentials

* Remove duplicate files

* Update namespace in program.cs

* Fix test build breaks

* Update extensions visibility.

* Remove unused resource strings

* Add xproj files to SLN for appveyor builds

* Fix appveyor build break in test project

* Fix extensibility tests

* Fix various typos in latest iteration

* Add settings for Integration build

* Fix codecoverage.bat to use full pdb for new projects

* Fix bug when packing in folder with native images

* Fix typos in xproj

* Reset XLF to fix build.cmd

src/Microsoft.SqlTools.ServiceLayer/project.json

@@ -33,7 +33,13 @@
     "System.Threading.Thread": "4.0.0",
     "System.Runtime.Loader": "4.0.0",
     "System.Composition": "1.0.31-beta-24326-02",
-    "Microsoft.Extensions.DependencyModel":  "1.0.0"
+    "Microsoft.Extensions.DependencyModel":  "1.0.0",
+    "Microsoft.SqlTools.Hosting": {
+      "target": "project"
+    },
+    "Microsoft.SqlTools.Credentials": {
+      "target": "project"
+    }
   },
   "frameworks": {
     "netcoreapp1.0": {