added a new index page for a pg/ug choice

* old index now moved to the list action
* index page defaults its year to the current year. Once the pg/ug choice has been made the year can be changed as needed by the user
added url() to links to get the right full url
fixed wrong link
Merge branch 'develop' of https://github.com/unikent/programmes-plant into feature/ug-pg-homepage
Merge branch 'develop' of https://github.com/unikent/programmes-plant into feature/ug-pg-homepage
exclude ug/pg specific links when on the home page
add year links to home page
Merge pull request #559 from unikent/feature/ug-pg-homepage

Feature/ug pg homepage