chore(karma): remove .js extension so imports work
chore(build): add serve task w/ livereload support

Running `gulp serve` will start a static server at localhost:8080, for
access to the root directory. Similarly, running `gulp serve --watch`
will start a server at localhost:8080 with livereload support, and
build/reload when files change.
chore(build): fix path resolution in styles task