Switching to referencing all ngrok packages with qualified names so that we can properly share this code as a library.

I wanted to use ngrok as a library to build a different version of ngrok without a lot of the features you've built in (e.g. don't need TCP tunnels or a local HTTP interface). But referencing any/all of the functionality of the project isn't possible given the layout of imports. So I switched it to be more in line with the Go workspace layout defined in the documentation: http://golang.org/doc/code.html#Organization.

Everything builds as far as I can tell and by using the canonical paths for things there's far less confusion about where things are hosted and what they're doing.