Disable the AnkiWeb sections from the Upgrade Wizard

*Please merge into 2.1*

Solves [Issue 1722](https://code.google.com/p/ankidroid/issues/detail?id=1722):
Disable the AnkiWeb sections from the Upgrade Wizard as they are no longer available.

I simply disabled the AnkiWeb buttons in the wizard and set the strings to "N/A". I have updated the Wiki page to make a note that the AnkiWeb mediated options are no longer available.