Cli termbox

This PR contains a rough implementation of the Sia client in Go. 

Instead of being asked for commands, the user selects commands from a list. Instead of asking the user to type input into the terminal and using 'fmt.Scanln' the user is prompted by a 'tbEditBox' and then 'fmt.Sscan' or 'fmt.Sscanln' is used to parse the input.

Things I need to neaten up (after i get some sleep):
-Document code a little better
-Find a better way to send messages to the user (the message boxes don't do this very effectively)
-Find a better way to output multi-line output (e.g. list of wallets or metadata)
-Give each command its own form (instead of prompting with multiple 'tbEditBoxes') by making an 'editBox' its own type/interface and coding a custom form for each command.

I honestly don't think this is quite ready to be added to the main repo yet, but wanted to show you what I have so far.
And by that I mean you need to create a client-curses.go that explains how your termbox application works and what the general conventions/shortcuts/etc are that you use.