Work around build issue for existing csproj's

Visual Studio tooling will use project.json to restore nuget dependencies
when it finds one beside .csproj. This change uses more specific
<project name>.project.json to specify dependencies.

BasicTest/BasicTest.project.json

+{
+  "runtimes": { "win": {} },
+  "frameworks": {
+    "net45": {
+      "dependencies": {
+      }
+    }
+  }
+}

MigratedBookSleeveTestSuite/MigratedBookSleeveTestSuite.project.json

+{
+  "runtimes": { "win": {} },
+  "frameworks": {
+    "net45": {
+      "dependencies": {
+        "NUnit": "3.0.0"
+      }
+    }
+  }
+}

MigratedBookSleeveTestSuite/packages.config

-<?xml version="1.0" encoding="utf-8"?>
-<packages>
-  <package id="NUnit" version="3.0.0" targetFramework="net45" />
-</packages>
\ No newline at end of file