Preloaded tags belonging to Projects and added a generic helper to generate link list

Since the app already used "tag_list" and did not preload the tags, there was the problem of the app hitting the database for every project to get its associated tags.

This patch preloads the tags using the `includes` method. 

Also the view code to render the tags - technologies and causes as a list of links has been re-factored into a single helper that handles both these types of tags.