Configure Grunt

* `makepot` task: generates .pot file in `i18n/languages/`
* `copy` task: copies files to `build` directory for WP deploy
* `clean` task: cleans unneeded files from `build` directory (files
that do not need to be checked into SVN)
* `wp_deploy` task: checks out WP.org SVN repo in a `tmp` directory,
commits “Tagging x.xx.x”, creates tag with version x.xx.x, commits
assets. Note: the version is automatically read from readme.txt and the
main plugin file
Add .gitignore
Add wp-assets dir

This directory will serve as the clone of the ‘assets’ directory on
WP.org SVN. Any changes made here will be deployed to SVN when running
`grunt wp_deploy`
Generate .pot file & update path