Colored bars

Ongoing work.
* colors could also be read from phpunit.xml configuration
* --colors wins over configuration
* Yellow bar for incomplete or skipped tests

How to test this? I can write a test with an expected output containing the escape characters for colors in the terminal, but it would not be readable and will mirror the code it is testing:
```
$this->assertEquals("\x1b[36;41m\x1b[2K...", $output);
```