Add gulp tasks to build deb packages

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

resources/linux/debian/code.desktop

@@ -0,0 +1,10 @@
+[Desktop Entry]
+Name=Visual Studio Code
+Comment=Code Editing. Redefined.
+GenericName=Text Editor
+Exec=/usr/bin/code %U
+Icon=code
+Type=Application
+StartupNotify=true
+Categories=Utility;TextEditor;Development;IDE;
+MimeType=text/plain;

resources/linux/debian/control.template

@@ -0,0 +1,10 @@
+Package: visual-studio-code
+Version: @@VERSION@@
+Section: devel
+Priority: optional
+Architecture: @@ARCHITECTURE@@
+Maintainer: Microsoft Corporation <vscode-linux@microsoft.com>
+Homepage: https://github.com/Microsoft/vscode
+Installed-Size: @@INSTALLEDSIZE@@
+Description: Code Editing. Redefined.
+ Build and debug modern web and cloud applications.