Add new mesamatrixctl CLI tool

This commit replaces the individual `tools/*.php` files with a single
`mesamatrixctl` tool that uses Symfony Console. This means pretty console
output, less boilerplate code, more flexible output etc. All commands are
found in `lib/console/command/` and are registered from the static method
in `lib/console/commands.php` (Mesamatrix\Console\Commands::register()).

This commit also brings the 3rdparty directory, containing the following
git submodule links:
 * Symfony Console: https://github.com/symfony/Console
 * Symfony Process: https://github.com/symfony/Process
 * PHP-FIG Log:     https://github.com/php-fig/log

These submodules need to be initialised before use of Mesamatrix, by running `git submodule init` followed by `git submodule update`

In addition, the autoloader was slightly modified to use proper case for
class paths as per PSR-0, with compatibility for the current all-lowercase
paths. Other minor changes were made to other files also.
What's PSR exactly?