Everyone likes new stuff

Major version changed due to inquirer.js changing its node version requirements. Plop 2.x now requires Node 8.9.4 or greater. There should be no breaking changes in the API itself.

• added optional data property for all actions that can be used in the template
• added force option for all actions with CLI ability to run actions forcibly
• added skipIfExists option for add and addMany actions
• added append action (similar to modify)