Set version to 2.0.0

Some parts of AgenDAV are going to be rewritten, starting with the DB
abstraction layer. This qualifies as a major change, so following
SemVer guidelines this should be tagged as 2.0.0
Require doctrine, and move DB config to config.php
Move preferences retrieval to its own repository

Still not functional, needs a new 'time' column on the prefs schema to
make the UPDATE actually work
Fix preferences storage when no changes were applied

When storing unchanged preferences the UPDATE query affects no rows,
so an INSERT is issued and fails because of duplicate primary keys.

This problem is fixed just by ignoring the INSERT error.
Use new preferences repository everywhere

Switch to the new preferences repository where the old preferences "model" was
being used
Use Http Foundation Session instead of CodeIgniter sessions

It still doesn't use Doctrine to store sessions, but now we do not depend
on CodeIgniter session handler.

Note: session options (inside advanced.php) have changed
Fix Vagrant cache issue

There are sendfile issues with Vagrant. Have a look at
http://stackoverflow.com/questions/9479117/vagrant-virtualbox-apache2-strange-cache-behaviour/9480164#9480164
Move session code to controllers, outside from User class

A lot of controllers were using 'user' to manage the current session.

These are the first steps to move it to better places.
Add missing dependencies

Seems that I messed up composer.json, and http-foundation wasn't listed.
Move DB connection code to its own class

The new CLI needs this connection, so following the DRY principle we are moving
DBAL initialization code to a new class.
Remove require restrictions on configuration files
Replace agendavcli with the doctrine CLI tool

Still not functional, but at least it connects to the database.
Switch to doctrine-migrations and symfony/console

This should fix all issues with CodeIgniter bogus CLI detection, which
shows HTML on console depending on your environment.

Migrations are now based on doctrine-migrations, so more DB drivers should
be supported now.

This commit adds required migrations to upgrade from 1.2.6.2, and migrations
required for a fresh installation.

Docs have to be updated.
Store sessions on DB again

Using symfont/doctrine-bridge this task is trivial.

Note that sessions are not being encrypted yet.
Encrypt session data

AgenDAV stores passwords on sessions, so now all data is encrypted using
the configured encryption key.

The algorithm used for encryption is AES-128.
Remove old *.sql files

Now the schema creation is managed by the agendavcli script, so these are not
needed anymore.
Update ansible rules to match new DB procedures

* Do not create a 'database.php' configuration file
* Load the DB schema using the new agendavcli script
Update README info about supported database engines
Remove old sessions code
Remove ancient "No direct access to this script"