options.include for makepot admin task

Added an `includes` option for the `makepot` task to specify which files should be scanned.
`grunt-wp-i18n` has now support for [options.include](https://github.com/blazersix/grunt-wp-i18n#optionsinclude)
Updated grunt-wp-i18n to 0.4.7 to support options.include
Merge pull request #6071 from axistools/makepot

options.include is now supported for makepot task