Previously developers had to install gulp globally on their machine
to build the project. These changes changes that by using the already
locally installed version of gulp, removing the environment requirements
aswell as ensuring everyone are using the same version of gulp.

It fixes the VS Code build tasks, aswell as creating a npm script to trigger the watch task:

```bash
$ npm run watch
```

As npm puts files from `./node_modules/.bin` in `$PATH` when running npm scripts, running bin commands from npm dependencies could be run directly, without a bin script deep inside `node_modules`.

P.S. great editor you've made so far!

fixes #2863

Port noUnexternalizedStringsRule to TS 1.8.0. Add support to detect duplicate keys with different messages

Build, install and run:
gulp vscode-linux-packages
sudo dpkg -i out-linux/vscode-amd64.deb
code .

Installing the package does the following:
- Puts VSCode dir at /usr/share/code
- Puts code.sh launcher in /usr/bin
- Defines a .desktop file to properly integrate with the launcher

Fixes #2679

related to #2785

Fixes #378

fixes #1998

Adding tslint and typescript as a dependency to satisfy the peerDependencies of tslint and gulp-tslint.