[TIMOB-11052] Win8: Implement validations in the demo app

Entry fields in the demo app should be validated. The user should be prompted with an AlertDialog if an issue occurs. Validation scenarios: 1) Any of the charge fields are not set on Add to Report click: Prompt "Please enter [field name]" 2) Date is in the wrong format or contains anything except digits and slashes on Add to Report click: Prompt "Date should be in mm/dd/yyyy format" 3) Transaction amount has invalid characters on Add to Report click: Prompt "Invalid transaction amount" 4) If the user clicks "Home" after editing the report (charges are added or any fields have values in them): Prompt "Are you sure you want to leave the page and lose all expense report changes?" Yes/No 5) Any of the report fields are not set on Submit Report: Prompt "Please enter [field name]" 6) No charges are entered on Submit Report: Prompt "Please enter charges"