Rework pagination UI

[kerberizer]

Backend now has additional fields numFound and start in /db/query response JSON:

{
  "status": 0,
  "numFound": 252,
  "start": 0,
  "response": [
    {
      (...)

Let's use this to rework our paging UI, aiming for a user-friendly look like in Template Designer with two small differences:

• keep the ability to set the number of results per page (so, compared to Template Designer, we need an additional UI element to set page size);
• keep showing the total number of results (numFound from above), though we'll need to determine where it will fit best in the new UI (could be "N hits found" as it is now, or we could move it to the pagination controls).

CC @vedina