V1.1 bugs fixed

1. Problem with date time -- done. Fixed with Convert.DateTime(date,
"en-US") which specifies that the date should satisfy "en-US" style.
2. File not exist in readMarketAccount and readBankAccount -- ensured in
the constructor. Code contracts are added in the set methods of
marketAccountFile and bankAccoutFile.
3. code cleanup -- done
4. exceptions in folder exceptions -- done