Provide way to easily initialize plugins

[robertpainsi]

It should be easy to add plugins like

• load and save the current filtering to hash
• no results info (toggle)
• custom plugins
• and many others

to the library, like plug and play. Just add the plugin during initializing filtering.js and everything else should work out of the box and automatically.

For now the first implementation will be experimental until enough data and differing use cases are gathered to provide a powerful but also flexible plugin system. In the future this should also be the preferred way to add functionality and will replace the current sub-classing and method overwriting approach.