New features and overall fixes

• Added backwards compatibility for determine_locale() function
• MFN Archive Widget: Added limit property to make it possible to decide how many reports to show in the list
• MFN News Feed Widget: Added "group by year" feature
• MFN News Feed Widget: Now the year list is populated depending on the current locale in WP which is more dynamic
• Updated plugin/widget descriptions
• Did some all around code refactoring/cleanup