Switch to StackExchange.Redis

This is a work-in-progress pull request for replacing the ServiceStack.Redis libraries with StackExchange.Redis. The main reason for this is future maintainability.

The Hangfire.Redis library was announced as deprecated by the creator of Hangfire, so this project aims to be the open source replacement.

Tasks:
- [x] Remove the NuGet package restore functionality from the solution. See this blog post for reason: http://mkchandler.com/disable-nuget-package-restore-on-a-solution/
- [x] Target latest version of [Hangfire.Core](https://www.nuget.org/packages/HangFire.Core/) ([which is still open source](https://github.com/HangfireIO/Hangfire))
- [ ] Replace [ServiceStack.Redis](https://github.com/ServiceStack/ServiceStack.Redis) (which is open source but you have to pay for usage) with [StackExchange.Redis](https://github.com/StackExchange/StackExchange.Redis)