Calendar - more accessible

[cbel]

To make the calendar portlet more accessible few things have to be done. (an issue have already be raise about putting days in TH, so here are the other modifications)

• month should be the Caption of the calendar table
• Identificate the current day in another way than only visual

[pjesi]

Another thing which would make the calendar portlet more accessible is to only load the calendar (using KSS) when next/previous month is selected.

[limi]

(In [16354]) Making the calendar more accessible:

• Adding the month as a hidden caption element
• Adding <strong> to indicate the current day in addition to the purely visual class it already has.

Hanno: I couldn't quite figure out how the translation of month names happen now, please check the <caption> tag and make sure it's translated.

This fixes #6022.