Template: clean+vanilla Ubuntu 12.04.3 desktop

New preseed.cfg + sane Vbox default settings + comments in preseed + definition

This template is loosely based on *ubuntu-12.04.3-server-i386* and  ***ubuntu-12.04.2-desktop-amd64***

###Main changes

- Reorganize preseed.cfg based on precise example+documentation
- Mess with partitioning and change disk size (smaller) to 30GB  (exports to 1.1GB box)
- Improve VirtualBox default settings for a desktop image and document
- Cleanup cruft

###Settings

-  **Version:**  Ubuntu 12.04.3 Desktop release
-  **Locale:** en_US
-  **Keyboard layout:** US
-  **Timezone:** UTC
-  **Extra Language Support:** none