Add image optimization automation to Gruntfile

[garrettdimon]

Right now, you have to manually run any images through an optimizer. It would be nice if this was automated with the upload process or as its own standalone task. (Or both.)

[derekrushforth]

This is a great idea. I'm all for automating the image optimization process. Here a couple plugins I found:

• https://github.com/JamieMason/grunt-imageoptim – I had a good experience using this one in the past, but it requires additional dependencies to be installed and would complicate the setup process.
• https://github.com/gruntjs/grunt-contrib-imagemin – Haven't used this but it looks promising. Comes bundled with the required optimizers which would make the setup process a breeze.