[Console] A better progress bar

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #9573, #9574, #10187, #9951, related to #9788
| License       | MIT
| Doc PR        | symfony/symfony-docs#3626


TODO:

 - [x] add some docs

See what this PR allows you to do easily:

![cwzpvk](https://f.cloud.github.com/assets/47313/2302190/30cd80e4-a170-11e3-8d88-80c4e4ca8b23.gif)

## New ProgressBar class

First, this PR deprecates `ProgressHelper` in favor of `ProgressBar`. The main difference is that the new `ProgressBar` class represents a single progress bar, which allows for more than one bar to be displayed at a time:

```php
use Symfony\Component\Console\Helper\ProgressBar;
use Symfony\Component\Console\Output\ConsoleOutput;

$output = new ConsoleOutput();

$bar1 = new ProgressBar($output, 10);
$bar2 = new ProgressBar($output, 20);
$bar2->setProgressCharacter('#');
$bar1->start();
print "\n";
$bar2->start();

for ($i = 1; $i <= 20; $i++) {
    // up one line
    $output->write("\033[1A");
    usleep(100000);
    if ($i <= 10) {
        $bar1->advance();
    }
    print "\n";
    $bar2->advance();
}
```

And here is how it looks like when run:

![progress-bars](https://f.cloud.github.com/assets/47313/2300612/4465889a-a0fd-11e3-8bc2-b1d2a0f5dc3d.gif)

## Format Placeholders

This pull request refactors the way placeholders in the progress bar are managed. It is now possible to add new placeholders or replace existing ones:

```php
// set a new placeholder
ProgressBar::setPlaceholderFormatterDefinition('remaining_steps', function (ProgressBar $bar) {
    return $bar->getMaxSteps() - $bar->getStep();
});

// change the behavior of an existing placeholder
ProgressBar::setPlaceholderFormatterDefinition('max', function (ProgressBar $bar) {
    return $bar->getMaxSteps() ?: '~';
});
```

Several new built-in placeholders have also been added:

 * `%remaining%`: Display the remaining time
 * `%estimated%`: Display the estimated time of the whole "task"
 * `%memory%`: Display the memory usage

## Formats

Formats can also be added (or built-in ones modified):

```php
ProgressBar::setFormatDefinition('simple', '%current%');

$bar->setFormat('simple');
// is equivalent to
$bar->setFormat('%current%');
```

Built-in formats are:

 * `quiet`
 * `normal`
 * `verbose`
 * `quiet_nomax`
 * `normal_nomax`
 * `verbose_nomax`

## Format Messages

You can also set arbitrary messages that depends on the progression in the progress bar:

```php
$bar = new ProgressBar($output, 10);
$bar->setFormat("%message% %current%/%max% [%bar%]");

$bar->setMessage('started');
$bar->start();

$bar->setMessage('advancing');
$bar->advance();

$bar->setMessage('finish');
$bar->finish();
```

You are not limited to a single message (`message` being just the default one):

```php
$bar = new ProgressBar($output, 10);
$bar->setFormat("%message% %current%/%max% [%bar%] %end%");

$bar->setMessage('started');
$bar->setMessage('', 'end');
$bar->start();

$bar->setMessage('advancing');
$bar->advance();

$bar->setMessage('finish');
$bar->setMessage('ended...', 'end');
$bar->finish();
```

## Multiline Formats

A progress bar can now span more than one line:

```php
$bar->setFormat("%current%/%max% [%bar%]\n%message%");
```

## Flexible Format Definitions

The hardcoded formatting for some placeholders (like `%percent%` or `%elapsed%`) have been removed in favor of a `sprintf`-like format:

```php
$bar->setFormat("%current%/%max% [%bar%] %percent:3s%");
```

Notice the `%percent:3s%` placeholder. Here, `%3s` is going to be used when rendering the placeholder.

## ANSI colors and Emojis

The new progress bar output can now contain ANSI colors and.or Emojis (see the small video at the top of this PR).