Add headline filter

In cases where you may have large numbers of nodes, it can be tedious to find the headlines you want to assign to an epublish publication edition.

This patch removes the existing filtering form, and calls the same filtering form used by the core node module.

So, instead of listing nodes on a page by page bases in some random order, you can select the desired category, or type of node, hit filter, and see a list of these, and then select the headline to assign.

1. Makes things consistant with other node listing filters
2. Makes the thing easier to use.

It's quite a small patch - but thought it might be helpful. This is my first ever patch, and hope I can contribute something more substantial in the future!

Thankyou.