change pathes in calendar/templates/* files to make them work with the new folder structure in /calendar/ajax

It´s automatically search in the owncloud folder and in the parent folder.
override with an option in config.php is also possible

for licensing information please have look at core/img/filetypes/readme-2.txt

Without this clients won't see the update because they compare ctags
before fetching the actual calendar to reduce traffic.

Signed-off-by: Florian Pritz <bluewind@xinu.at>