MDL-18375 calendar: added multiple calendar support

Conflicts:

	course/edit_form.php
	lib/db/install.xml
	lib/form/dateselector.php
	lib/form/datetimeselector.php
	lib/setup.php
MDL-18375 calendar: removed calendar systems that should be downloaded as plugins
MDL-18375 calendar: moved the calendar systems location to a sub-folder in the calendar directory
MDL-18375 calendar: removed Non-English language for the Gregorian calendar system that should be downloaded separately

Also removed unnecessary version.php file.
MDL-18375 calendar: removed custom files responsible for checking for updates as this should be done through core
MDL-18375 calendar: removed JS as there is no non-JS alternative provided and the JS does not make use of the YUI library to ensure multiple browser support
MDL-18375 calendar: changed the class name to reflect the new directory location and added PHPdocs