caldav: add MKCOL support

caldav/elements.go

@@ -228,3 +228,10 @@ func (r *reportReq) UnmarshalXML(d *xml.Decoder, start xml.StartElement) error {
 
 	return d.DecodeElement(v, &start)
 }
+
+type mkcolReq struct {
+	XMLName      xml.Name              `xml:"DAV: mkcol"`
+	ResourceType internal.ResourceType `xml:"set>prop>resourcetype"`
+	DisplayName  string                `xml:"set>prop>displayname"`
+	// TODO this could theoretically contain all addressbook properties?
+}