Some options moved to locale files + other fixes

- first_day and enable_easter_holidays now may be specified also in language files
- added all the currently available languages to the example page (and sorted them alphabetically)
- added default first_day/enable_easter_holidays to language files
- added two missing translations in French (Easter/Easter Monday)
- fixed an error in sv-SE file (a required comma was missing)
- added comments to the language template