Also move iCalendar patch; describe dependencies in README files

plugins/calendar/README

@@ -10,15 +10,14 @@ The client-side calendar UI relies on the "fullcalendar" project by Adam Arshaw
 with extensions made for the use in Roundcube. All changes are published in
 an official fork at https://github.com/roundcube/fullcalendar
 
+For some general calendar-based operations such as alarms handling or iCal
+parsing/exporting this plugins requires the `libcalendaring` plugin which
+is also part of the Kolab Roundcube Plugins repository. Make sure that plugin
+is installed and configured correctly.
+
 For recurring event computation, some utility classes from the Horde project
 are used. They are packaged in a slightly modified version with this plugin.
 
-iCalendar parsing is done with the help of the Horde_iCalendar class. A copy
-of that class with all its dependencies is part of this package. In order
-to update it, execute lib/get_horde_icalendar.sh > lib/Horde_iCalendar.php
-Finally apply the patch lib/Horde_iCalendar_timezone.diff to fix timezone
-handling when parsing iCal files.
-
 IMPORTANT
 ---------
 The calendar module makes heavy use of PHP's DateTime as well as DateInterval

plugins/libcalendaring/README

@@ -0,0 +1,15 @@
+Library providing common functions for calendar-based plugins
+-------------------------------------------------------------
+
+Provides utility functions for calendar-related modules such as
+
+* alarms display and dismissal
+* attachment handling
+* iCal parsing and exporting
+
+iCal parsing is done with the help of the Horde_iCalendar class. A copy
+of that class with all its dependencies is part of this package. In order
+to update it, execute lib/get_horde_icalendar.sh > lib/Horde_iCalendar.php
+Finally apply the patch lib/Horde_iCalendar_timezone.diff to fix timezone
+handling when parsing iCal files.
+