Updated build-dependencies and changed their order
Debug mode is now determined by a global var which gets removed by uglifyjs, instead of using a string replacement method
Split up the build task (resolves #5):

- `build`: builds the app inside the `/build/tmp` folder and generates sourcemaps. Due to the usage of node-webkit's `app://` protocol, all contents have to embedded to the sourcemaps instead of being referenced (can't leave the root folder). This means that contents cannot be edited from inside the dev-tools.
- `dev`: runs the build task and starts a separate watcher task for less and javascript files.
- `release`: builds the app with release settings inside the `/build/tmp` folder and compiles it.