WebSearch: introduce next/previous/back links
- Introduces next result, previous result, back to search links on the detailed record pages. The behaviour can be influenced by variable CFG_WEBSEARCH_PREV_NEXT_HIT_LIMIT. (closes #454)
- Notably tested cases such as user displays results in a single list, user displays results split by collections, user introduces the URL of only one record, option "sort by" is choosen, accessing a detailed record URL having not done any search before.