Ability to specify own set of supported calendar component set.

Drawback: now it is required to explicitly specify `'{urn:ietf:params:xml:ns:caldav}supported-calendar-component-set'` property on each calendar.

Example:
```javascript
var SCCS = require('./node_modules/jsDAV/lib/CalDAV/properties/supportedCalendarComponentSet');
var jsCalDAV = require('./node_modules/jsDAV/lib/CalDAV/plugin');
// ...

var properties = { ... };

properties['{' + jsCalDAV.NS_CALDAV + '}supported-calendar-component-set'] = SCCS.new([ 'VEVENT' ]);
```