First pass at a WP-CLI command to install all the plugins
Make types more robust and add --activate flag

* Instead of hard-coding the types, use `get_project_types()` from
the developer plugin class
* Add the `--activate` flag to make plugin activation optional
Rename class to Developer_WP_CLI_Command
Merge pull request #48 from joshbetz/master

First pass at a WP-CLI command to install all the plugins