Fix debian build.

* Fix lintian errors.
* Update dependencies to work with sbuild
* Add debian/copyright
Restyle .travis.yml.

* Update travis.yml to rely on a basic set of commands, and not on those shitty
  build scripts.
* Remove useless commands in the script section.
* Re-order other commands, like `apt-get update` in before_install (as suggested
  by travis doc), `apt-get install` only in the install directive, etc.