speed up the popularity/movers update by running bulk queries (bug 1059964)

Fixes [bug 1059964](https://bugzilla.mozilla.org/show_bug.cgi?id=1059964)

The idea is to do a "bulk update" using a temporary table. We can then
```sql
UPDATE personas, tmp_table
SET personas.popularity = tmp_table.popularity,
        personas.movers = tmp_table.movers
WHERE personas.id = tmp.personas_id```
Will we switch to `ThemeUpdateCount` at some point, or will we need this "proxy" model even when in prod?