Fix build command for Windows

[Robert-W]

running mkdir -p on some windows machines seems to throw an error about the syntax not being correct. And also a fellow dev had no success with the r.js command until she changed it to r.js.cmd.

I will test r.js.cmd on Mac and if it works will update the builds and see about an alternative to mkdir -p if it becomes an issue.

Also not using gulp task babel:polyfill which is needed for older browsers like IE <= 9, so I need to simply add that to the gulp build and gulp dist commands.

[Robert-W]

Babel-polyfill command has been added.
r.js.cmd fails on Mac, so there is now distWin which uses r.js.cmd and can be used to resolve mkdir issues if necessary. npm start should be fine on windows but is still untested.