Integrating our code into upstream

[ulvida]

There have been too many changes (and some quite unhappy choices, see #3) in our master branch to be proposed as such to the unpstream role.

As the upstream role team is interested in our possible contribution (see stuvusIT/sympa issue #8), I created an upstream-master branch, started to progressively integrate and clean our code, in order to propose it step by step.

I start with PostgreSQL integration, as they expressed interest in this feature.

[ulvida]

I work in issue2-upstream branch.
First step (commit bf26fe6) to separate database tasks in another tasks file.
BTW, I propose some requirements checking and an option to install MySQL in the role itself.

[ulvida]

Next step: Apache configuration with the role. Our code in master branch is quite clean (albeit some configurations may be quite verbose). Let's integrate it progressively (and optional, to be backwards compatible).

Waiting for last PR acceptance, I open a new branch