[WIP] Default calendar view per user

This piece of work is almost complete I think. It adds a new field to the User Preferences area allowing each user to decide which Calendar View they want as their default, e.g. List, Shared or Calendar. We get asked to do this for almost every customer we have so it seems like a sensible idea to add it into the standard product.

I need help from vtiger however with two things:

1. The naming of the field label... There is already a field called 'Default Calendar View' but this is to decide if you want Day, Week, Month or Year display within the Calendar View itself.

2. Translations once the label is determined.

Thanks