Add `stack build --prefix` option

[borsboom]

This new stack build option will add a post-build step that rebuilds the targets with a cabal configure --prefix= option in a separate dist directory. This will allow installing packages that use data-files in a fixed location on the file system outside of any stack-controlled sandbox.

[borsboom]

In order to support installation into directories where the user doesn't have write permission (e.g., /usr/local), should support a flag to specify a command to prefix the Setup.hs copy step with (e.g., sudo). Before starting, check whether writing to the destination works, and if it does not, display a friendly error with a suggestion to use the prefixing option.

[borsboom]

Make sure this covers the case outlined in #1262 (comment)

[mgsloan]

Seems like this issue is cropping up for multiple people. Bumping to P2