Haskell REPL with cabal-dev support

I've implemented simple 'GHCi' command in SublimeHaskell, which loads GHCi on cabal or cabal-dev (depends on SublimeHaskell's settings). This setting is widely used in SublimeHaskell and can't be moved anywhere else.

But this command don't work with LoadFileToREPL, which uses default SublimeREPL command to open repl.

'GHCi' command from SublimeHaskell just calls repl_open with all the same args except 'cmd', which is ['ghci', '-package-db', path_to_package_conf] for cabal-dev and ['ghci'] otherwise, where path_to_package_conf depends on SublimeHaskell's setting.

I think, it'll be good, if SublimeREPL will try to load SublimeHaskell's settings and use them.

This pull request implements such command, but I don't know if it's a good solution.