ENH: factorized prepush and check-valid

`check-valid` now can specify options in a config file.

- useNewer: true. Whether to use grunt-newer to only check changed files
- tasksToRun: 'jsbeautifier,jscs,jshint,jsvalidate' which tasks to run as part of the `check-valid` task
- filesToValidate: what files to validate (an array of globs like: ['src/**/*.js']) By default will use the same files on the filesToValidate Object from common-config.js file.
- forceBeautify: true. By default the files will be beatufied automatically. If this is set to false. The task will break on the first file that needed beautification.

Same as `check-valid` but
- useNewer: is false by deafult
- forceBeautify: is false by default.