collection specific script

[kjdon]

To add collection specific javascript, currently you need to add _pagescriptextra_ to extra.dm. But some macro files define stuff in pagescriptextra and if you don't remember to include this in your version, then the pages don't work. I propose another macro, eg _collectionspecifcscript_ (we already have _collectionspecificstyle_) which can contain just the collection stuff

[kjdon]

I have added _collectionspecificscript_.

Also added empty _collectionspecificscript_ and _collectionspecificstyle_ macros into modelcol extra.dm so that the users will know about them.