HOLIDAYREQ-15 HOLIDAYREQ-16 HOLIDAYREQ-17 HOLIDAYREQ-18 HOLIDAYREQ-19: Refactoring of the Application

 - Addition of a "Comment" field to allow the manager to justify his
   choice (mandatory if refused)
 - Addition of a "Type of holidays" field (Normal, Unpaid, Medical
   holidays)
 - Change "Days" property type to Float
 - Improvement of the mails sent to managers and employees (Add comment if
   the request if refused, add text mail)
 - Improvement of the Skin extension
 - Correction of an issue with the Overview page when an user account was
   deleted
 - Correction of some French translations
 - Addition of a Calendar which shows the accepted requests of the
   selected week
[Misc] Align POM with best practices