Remove "by puzzle" view and enable meta reordering

[jpd236]

• Ensures that puzzles are always sorted by meta
• Add ability to reorder meta groups on page

[jpd236]

For the first request, the "By Meta" view is now the default view. I decided to keep the other view around as "All Puzzles" rather than get rid of it - it has a few functions for sorting and filtering that may be useful and don't quite fit as neatly into the "By Meta" view, so I'm hesitant to just scrap it altogether.

I've also implemented some rudimentary meta reordering. Each meta has move up/down links above its list of puzzles. There's a confirmation dialog you have to click through so that people are hopefully less likely to do this by accident, since (like other things) the site isn't really built to have more than one person adding/editing puzzles at once, aside from entering solutions.