Change the representation of the package database

Change the representation of the package database

 - the package DB is a directory containing one file per package
   instance (#723)

 - there is a binary cache of the database (#593, #2089)

 - the binary package is now a boot package

 - there is a new package, bin-package-db, containing the Binary
   instance of InstalledPackageInfo for the binary cache.

Also included in this patch

 - Use colour in 'ghc-pkg list' to indicate broken or hidden packages

   Broken packages are red, hidden packages are

   Colour support comes from the terminfo package, and is only used when
    - not --simple-output
    - stdout is a TTY
    - the terminal type has colour capability

 - Fix the bug that 'ghc-pkg list --user' shows everything as broken