Add support for using user secrets

[abcdefg30]

Removes the need to change appsettings.json to locally run the bot.

Right click on the Orabot.Hosts.ConsoleHost project and select Manage User Secrets:

Then you can put the bot token inside there like this

{
	"BotToken": "token"
}

[penev92]

Specifying user secrets as a configuration source feels like an implementation detail rather than a core "contract" detail (which is why you've used it in Orabot.Core and not Orabot.Core.Abstraction. Did you have a reason to add the package to the Abstraction project and not the implementation one?

[abcdefg30]

Yes, because I can't use AddUserSecrets otherwise which is an extension method from that package.

[abcdefg30]

Fixed.