Adding react-tools as dev dep.

Right now `gulp` failes if `react-tools` isn't installed globally. I feel it should either 
1) Be declared as a dev dep, as per this PR
or
2) Gulp task should try/catch the `require('react-tools')` and throw an error if it isn't found.

I know they recommend to install `react-tools` globally, but I haven't experienced any problems running it with a local installation