Add nuget dependencies config file

Author: lucasg

Dependencies/packages.config

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="Newtonsoft.Json" version="11.0.2" targetFramework="net461" />
+</packages>

appveyor.yml

@@ -41,6 +41,8 @@ deploy:
       platform: Any CPU
       appveyor_repo_tag: true       # deploy on tag push only
 
+cache:
+  - packages -> **\packages.config
 
 build:
   project: C:/projects/dependencies/Dependencies.sln
@@ -57,6 +59,9 @@ before_build:
         &secure-file/tools/secure-file -decrypt "C:/projects/dependencies/DependenciesAppx/DependenciesAppx_TemporaryKey.pfx.enc" -secret "$($env:certsecret)" -out "C:/projects/dependencies/DependenciesAppx/DependenciesAppx_TemporaryKey.pfx";
       }
 
+      # download all the necessary packages
+      nuget restore 
+
 after_test:
  - ps: |
       if ( $($env:platform) -eq "Any CPU") {