Reminder to save changes, better support for unusual currency symbols, long weekly stays bug fixed

A few little changes released this morning:

1. We now warn you if you change something on a booking and try to navigate away without saving. We've had that warning on the accommodation settings screen for a while, but not on the bookings screen. It's now on the bookings screen too, so if you change something on the booking screen (and don't save) you'll be prompted to save when you try and leave that page.

2. Some currency symbols, e.g. for the Thai Baht, were not displaying correctly on the PDF invoice for a booking. That's fixed now.

3. Finally, there has been a long-standing bug whereby if you were taking weekly bookings only, a guest couldn't book on the widget for more than 4 weeks (even if your max stay setting was, say, 90 nights which is about 12 weeks). That's fixed now.