Adding Packagist statistics for repo via Poser badges

Related to https://github.com/Behat/Mink/issues/421
Merge pull request #422 from aik099/packagist-badges-feat

Adding Packagist statistics for repo via Poser badges
Added some integration tests for the NamedSelector XPath queries
Change element location rule to evade Zombie error during form reset
Merge pull request #433 from aik099/simple-form-test-zombie-fix

Change element location rule to evade Zombie error during form reset
Merge pull request #432 from Behat/named_selector_tests

[WIP] Added some integration tests for the NamedSelector XPath queries
Mock SelectorsHandler in Element tests to break dependency on NamedSelector
Merge pull request #443 from aik099/mock-correct-party-in-ElementTest-phpunit-mocks-fix

Mock SelectorsHandler in Element tests to break dependency on NamedSelector
Adding tests to cover all xpath-related matching logic in NamedSelector
Merge pull request #442 from aik099/namedselector-matching-tests-part2-feat

Adding tests to cover all xpath-related matching logic in NamedSelector
Improves readability of NamedSelector xpath expressions
Merge pull request #438 from aik099/improve-readability-of-namedselector-feat

Improves readability of NamedSelector xpath expressions
Excluding input type=button/reset from `field` selector in NamedSelector

Also removing duplicate xpath code from `button` and `link_or_button` selectors.
Merge pull request #446 from aik099/inconsistent-namedselector-xpath-matching-fix

Fixing inconsistencies in NamedSelector xpath expressions
Sending coverage information to Scrutinizer and displaying badges
Merge pull request #448 from aik099/enable-scrutinizer-code-coverage-feat

Sending coverage information to Scrutinizer and displaying badges
Ensure all components of a union query are prefixed #340.
Added test for union queries in Element::findAll().
Wrap parent xpath in parentheses if it contains a union.
Enabled testing on HHVM on Travis