User notes and custom items

[lostcarpark]

Allow users to enter personal notes on program items. Expanded item could have a textbox where users could enter their own note.

Allow people to enter their own custom items, which could be used for lunch appointments, dinner dates, parties, or other things they're doing during the convention. I suggest restricting it to the dates of the convention, possibly adding a day either side. I don't think we want people turning it into their own personal calendar.

Note: JavaScript localStorage allows a maximum of 5MB per application, which ought to be plenty, but may need to keep an eye on how much we let people store in personal notes/appointments.