Upgrade to latest Grunt

Hey, I've updated lineman to use all the latest grunt tasks (which are all in the release candidate phase of the 0.4 release).

Note that this is a pretty big change. Most configuration in 0.3 is not compatible with 0.4. That said, everything seems to work. I think it makes sense to go for it.

A summary of the changes is in the commit message for 7bd9c9e, quoted below:

This updates lineman to the latest grunt, and also updates all of the
grunt tasks we use. Here's a quick summary of what I had to do:

 * grunt.utils has become grunt.util -- it's a little sad that this had
 to change in so many places :(

 * The grunt-contrib meta-package doesn't exist (apparently?) for grunt
 0.4, so now we explicitly depend on each grunt plugin that we use.

* The <config:propname> syntax has been replaced with <%= propname %>

* Banner configuration has moved.