Add userAgent to URLRequestTest
Add userAgent to openfl/net/URLRequest
Add userAgent to URLRequest in native and html5 backends
Add flash extern for URLRequest to noop userAgent
Add Lib extern to show that it causes tests to hang. Hoping for input from @jgranick
Remove the flash backend Lib override
Change flash backend openfl.Lib from typedef to wrapper to add notImplemented method.  Use notImplemented method in URLRequest
Formatting
Merge pull request #250 from JandyCo/urlrequest-user-agent

Add userAgent to URLRequest