chore(build): switched build system to Gulp

Fixes #38 

Changes:
- Replicated the build system using Gulp.
- Added "serve" task to spawn a webserver
- Webserver will listen for changes and auto-reload using liveReload
- Fixed https://docs.angularjs.org/error/$location/nobase
- Added correct 404 template

Todo:
- [x] Karma unit test task
- [x] Eslint linting task
- [x] Remove Gruntfile and Grunt dependencies

Run `gulp serve` to spawn the webserver and browse to `http://localhost:9000/example`.
All changes made in either the `example` folder or `src` folder will automatically reload the browser page.

No LiveReload browser extension required, gulp-connect uses https://github.com/mklabs/tiny-lr.
same here