Pluginify: remove plugins prior to transpiling

This changes `makeOrderedTranspiledMinifiedGraph` to accept a `prefilter` option. Prefilter is a function that is run against the graph data prior to ordering, transpiling, and minification. This is necessary because with pluginify it needs to remove plugins prior to any of these actions being performed.

The result is that no plugins are included in the built JavaScript file.

Fixes #42