Optimize storage for variables of Availability Calendars

We have some 8 settings per node stored in the variables table and 10 or so system wide. Most are used during rendering the calendar and are all read at once. Moreover we have one function that takes care of reading all these settings at once and this is about the only way the code accesses the settings.

So it might be better to store these in an array and save them in 1 variable. This will reduce the number of records for our module in the variables table by some 80-90%.