Coveralls.io travis settings and phpunit

Related to https://github.com/yiisoft/yii2/pull/664#issuecomment-21668074 (comment1) and https://github.com/yiisoft/yii2/pull/664#issuecomment-21673435 (comment 2)

Steps to be taken before merge:

 * Go to https://coveralls.io/ and activate the github hook there

I have not added the badge yet, as 57% coverage seems a bit low, so this should be investigated/fixed first before advertising with coverage ;)

The list of ignored files in phpunit.xml.dist should be adjusted, as more tests are added (HelperBase classes are still in the report, coverage of empty classes seemed to vary based on travis-php-version, so I ignored them for now, however last build showed them just fine, issue might be fixed)