Add css optimization to dojo builds

The important bit here is in rebuild-dojo.sh where I added cssOptimize=comments. This will take all the @include statements of claro.css and inline those files, resulting in one single claro.css file. This reduces the number of CSS files downloaded on page load from 45 files to 3 files. It also reduces the total download size of CSS files from 50K to 22K. Unfortunately, running the dojo build script touched a lot of other files so let me know if I should reduce this changeset to just the rebuild-dojo.sh file if you'd like to run the dojo build yourself before pushing to master. I did add a couple lines to automate the download and extraction of the latest dojo src code. So you can see exactly what steps I took.

Note you can also do cssOptimize=comments.keeplines in order to prevent the removal of new line characters in all css files.