Fix wrapping inside CLI prompts

* Fixes long questions wrapping badly
* Normalises the length of progress bar block to match question block
* Adds terminal width detection where appropriate to scale out

Before:
![before](https://cloud.githubusercontent.com/assets/237866/5234984/6e2e884c-77e0-11e4-9353-e31eaa68948a.gif)

After:
![after](https://cloud.githubusercontent.com/assets/237866/5234990/8fbf7ea8-77e0-11e4-8693-98bdf7c190b6.gif)

For future:

* Other blocks could read width from IO
missing visibility