Moving to latest NuGet packages for dependencies

Updates common dependencies to the latest available on NuGet.

```xml
  <package id="Microsoft.Bcl" version="1.1.6" targetFramework="portable-net45+sl50+wp80+win" />
  <package id="Microsoft.Bcl.Async" version="1.0.165" targetFramework="portable-net45+sl50+wp80+win" />
  <package id="Microsoft.Bcl.Build" version="1.0.13" targetFramework="portable-net45+sl50+wp80+win" />
  <package id="Microsoft.Net.Http" version="2.2.18" targetFramework="portable-net45+sl50+wp80+win" />
  <package id="Newtonsoft.Json" version="5.0.8" targetFramework="portable-net45+sl50+wp80+win" />
```