Check if install possible before building

* Add symlinkableBinary
* Extract installExesPrep
* Add data InstallExe and data Symlink
* Replace symlinkable with symlink taking InstallExe
* Replace symlink/copy as symlink or copy
* Improve a haddock, from check to try and stop
* Get rid of duplication between install*Exes
* Add InstallCfg
* Drop the cfg prefix
* Make errorMessage a where nested local
* Add haddocks to InstallCheck