Setup Karma testing framework

This pull request installs Karma and converts the existing tests to Jasmine tests.  `grunt test` does continuous testing, and `grunt test:unit` does a single test run.

Because the files needed to be concatenated before running tests, the `grunt test` task first runs a new `concat` task that creates a temporary dimple.js file, which is then used in the tests.

Next step is to write tests for the rest of the package.