SimpleCov added

SimpleCov is a code coverage analysis tool that generates awesome reports after running our test suite.
introduce gemset-specific simplecov filters

This also includes a SharedHelper to share
some settings between test_helper and spec_helper.
More filters for SimpleCov added

config, spec und test directories filtered
Groups for SimpleCov added
Coveralls added
allow local coverage generation w/o coveralls

When coveralls is not used (rake task) we should
still generate local simplecov reports.
Only load Coveralls if its rake task is invoked
Merge pull request #668 from ontohub/simplecov

Integration of Coveralls.