Address performance issues on front page

This takes a number of stragegies:

* **Don't `populate` programs for issuers.** We aren't using them, and populations are expensive.
* **Only pull the data we need from the database.** For badges, that's `name`, `shortname`, and `program` (for population). For issuers, all we need is `name`.
* **Implement cheap pagination.** I set a default of 50 items, added some "next" and "previous" buttons to the frontend and called it a day. I also added a "show all" link to revert to previous behavior of listing everything. Ideally, I'd also add a search functionality but this is quick & dirty optimization, not perfect.