Update pull request base branch

Update pull request base branch from `master` to `develop` in the contribution instructions.
Adding latest unstable release and license badges
Replace Travis CI and HHVM badges with SVG versions
Merge pull request #103 from aik099/102-use-svg-versions-of-all-badges

Replace Travis CI and HHVM badges with SVG versions
Adding "PageFactory::setSession" method
Merge pull request #105 from aik099/page-factory-set-session

Adding "PageFactory::setSession" method
Updating dependencies
Rearranging badges
Updating dependencies to reflect Mink 1.6 release
Due Behat/Mink#603 the `waitFor` method was waiting 1000 times longer
Adding AbstractFormElement marker class