[tasks] Introduce `packer` installation
[tasks] Update comments & rename template
[tasks] Introduce `apt-cacher-ng`
playbook: Add `xclip` package for ubuntu

This package allows copy & paste on the CLI (like `pbcopy` on Mac OSX)
ruby: Cleanup tasks & remove unneeded code
vim: Remove duplicated code
playbook: Install `exuberant-ctags`
thunderbird: Setup and configure