Caching of index pages

As rendering the index pages can be a relative large performance hit especialy when creating threaded lists I decided to cache index pages if the administrator wants it. At the moment the entire page is saved into the database. This includes all the markup, so when you have changed your template files you'll need to clear the cache. This can be done in the Vocabindex admin section.

Issue is fixed and committed to 6.x-2.x-dev