Support removing old build plans

[kseo]

It would be nice if I can see the list of installed build plans and remove old ones using stack command. Old build plans take up too much space of my disk.

Removing files under ~/.stack/ is too error-prone.

http://stackoverflow.com/questions/39227397/how-to-remove-old-build-plans-installed-by-haskell-stack

[decentral1se]

Removing files under ~/.stack/ is too error-prone.

In this case, in the global project, it might be a bit tricky? Build plan files seem to be mixed around the place. However, for isolated projects, you are aware you can simply do a ls .stack-work/install/<os>?

I like the idea though, what would that interface look like? An argument on what Stack command? Would be nice on stack clean but doesn't fit (only for packages). Doesn't seem to fit on stack build either?

[mgsloan]

Duplicate of #133