(bug 18195) Allow changing preferences via API

(bug 18195) Allow changing preferences via API

I have created an API module for changing the preferences.
It allows resetting preferences (reset argument) and bulk changes
of preferences (change argument) in a format:
name1=value1|name2=value2

The change argument has a limitation imposed by the current API
implementation as it cannot accept | in values. There is
available a pair of arguments optionname and optionvalue, the
latter accepts values with |.

I have created optionstoken parameter in meta=userinfo to provide
a token. There is already preferencestoken there, but I would
like to have a consistent naming.

Change-Id: I0d6c654a7354ba77e65e338423952a6a78c1150f