Lint .feature files

Test 1: Test no lint errors exist.

1. npm install
2. grunt gherkinlint
3. Ensure you don't see any behat lint errors.

Test 2: Sanity check.

1. Go though the patch and ensure changes are not modifying scenario steps. Only:
   • Indentation
   • Feature name/description

Test 3: Test gherkinlint is executed during watch

1. Execute grunt watch
2. Modify some feature file and save
3. Check the modifications in feature file are reported by grunt watch

Test 4: Test gherkinlint is executed by grunt

1. Execute grunt
2. Check gherkinlint task is executed.