Slim packer scripts, sharing most of them for both ubuntu 12.04 and 14.04.

(I can only test on ubuntu 12.04 now, and it works!)
* Move almost all packer scripts to a shared directory appliance/scripts
* Prefix every executable script with /bin/sh (bash is not necessary for now)
  and run them properly from inside template.json.
* Give more appropriate names to scripts.
Place informative comments around all this pip shitty hack.
Add debian 7.7.0 packer script.

It's working, yay! Fixes #496.
Update ubuntu-14.04 packer scripts to rely on this pip build.
Add preinst-globaleaks.sh script, FWIW
Add libssl-dev as dependency to have ubuntu-14.04 working the new postinst.

Pip was complaining of no openssl/aes.h to include.
Use bower when building client, in travis.yml file.
Disable client test 004, to work around #1017 until gets fixed.