Coverage summary for PHPUnit plugin #148

Add coverage summary for PHPUnit plugin (See #86). Description by @SimonHeimberg:

Showing the summary (with phpunit ... --coverage-text reportFile.txt ... and then grep --max-count 3 '% ' reportFile.txt [1]) or even including this 3 values [1] in the graph would still be great.

[1] The 1st 3 values (with %) are the total coverage of Classes, Methods and Lines.