Use different ghci command

[Genora51]

The Load GHCi button currently runs stack ghci, but when run outside a stack project, this warning is output:

Warning: No local targets specified, so ghci will not use any options from your package.yaml / *.cabal files.

         Potential ways to resolve this:
         * If you want to use the package.yaml / *.cabal package in the current directory, use stack init to create a new stack.yaml.
         * Add to the 'packages' field of /Users/geno/.stack/global-project/stack.yaml

Should the command run instead be stack exec -- ghci?

[matobet]

Ideally the ghci command should be configurable so this could be overridden for projects that use plain Cabal.