Integrate GitHub library for updating

[gbakeman]

Introduction

The current method of updating involves making an HTTP request to GitHub, parsing the response, then displaying the raw markdown release info in a text box. There are a few ways to improve this:

Goals

• Modularize underlying update code; extract it from the Update Form code into extendable code in the common library
• Replace manual HTTP request method with a GitHub API library from NuGet

Related

Part of: #97