Produce dist from Gulp

This PR allows to run:
```bash
gulp --dist
```
It does the following:
- it only runs the `dist` task,
- it changes the `dest` variable from `./build` to `./dist`,
- it excludes from the vendor bundle the packages listed in the `pruneVendors` config parameter (`angular-mocks` in our case).

Note: it fixes issue #21