Localization of date labels using Sugar locale support

First attempt to localize the date formats of the X-axis labels, using Sugar *locale* support. This avoids the definition of the long and short month names.

For changing locale, one has to define e.g. ```Date.setLocale('en');``` at the beginning of the js/gneisschart.js file. This could be made a dropdown in the UI.

PS. Also, added a new date format *ddM* used in European countries.