Create list of available items via API, instead of hardcoding numbers

[blarz]

At the moment, all items and their corresponding numbers are hardcoded in menu.py (see USER_KEY_CONSUME_*).

We could use the /items GET call, to receive a list of all available items and generate the menu of "consumables" programmatically instead of hardcoding the numbers. Would make heiko more flexible if we add/remove items in the future (think "Pizza" for the CCCamp..).

[blarz]

Hardcoding the keys also means, that if your database on the server side doesn't have the exact same item ids as described in menu.py, this will fail.

I'll look into this soon hopefully.

[noqqe]

Would really appreciate this!