Add a setting to hide CardDAV section from preferences
Remove unused attribute
Add a per-preset option to hide it from preferences

A new option ('hide') for presets makes them not to show on the CalDAV
settings section.

If 'hide_preferences' is disabled, all presets are shown by default
unless they have the 'hide' option set to true.
Fix indentation on config file
Merge branch 'hide_settings' of git://github.com/adobo/rcmcarddav into adobo-hide_settings
two little hotfixes for the check if addressbooks should be hidden