Restructure number cells to allow other elements

To pave the way for week number display in the day cell, the number
cell is changed so that it can contain more than only the day number.

src/basic/basic.css

@@ -36,7 +36,7 @@
 }
 
 .fc-basic-view td.fc-week-number span,
-.fc-basic-view td.fc-day-number {
+.fc-basic-view td.fc-numbercell span {
 	padding-top: 2px;
 	padding-bottom: 2px;
 }
@@ -52,14 +52,14 @@
 }
 
 .fc-ltr .fc-basic-view .fc-day-number {
-	text-align: right;
+	float: right;
 }
 
 .fc-rtl .fc-basic-view .fc-day-number {
-	text-align: left;
+	float: left;
 }
 
-.fc-day-number.fc-other-month {
+.fc-numbercell.fc-other-month {
 	opacity: 0.3;
 	filter: alpha(opacity=30); /* for IE */
 	/* opacity with small font can sometimes look too faded

src/common/DayGrid.js

@@ -143,11 +143,13 @@ var DayGrid = FC.DayGrid = Grid.extend(DayTableMixin, {
 		}
 
 		classes = this.getDayClasses(date);
-		classes.unshift('fc-day-number');
+		classes.unshift('fc-numbercell');
 
 		return '' +
 			'<td class="' + classes.join(' ') + '" data-date="' + date.format() + '">' +
-				date.date() +
+				'<span class="fc-day-number">' +
+					date.date() +
+				'</span>' +
 			'</td>';
 	},