Increase timeout of css assets tests failing on Travis.

Some tests regularly fail on Travis CI when running on Node 0.8 because the running time exceeds the mocha default timeout of 2s. Increasing this to 10s for the failing tests.
Move devDependencies to dependencies. Except Mocha.

For installable modules referenced in a package.json, which xtc is now, npm only installs dependencies. Therefore everything needed for building and running the server needs to be in dependencies. Which is the way it should be anyway.