Safer bulk actions

We're currently working on making bulk actions clearer and safer to prevent accidental mishaps:

1. Selection text now clearly shows whether you're selecting specific items or everything except a few items.
2. Selected items are now shown during confirmation.
3. High-risk actions now require typing a random 3-word phrase to proceed.

Right now, some of these improvements are only applied to deleting subscribers and emails. We're continuing to roll out these changes to all bulk actions.

As always, feedback welcome.