Fiscal year autofetch added

Solution for Issue #733

-> New DocType - Fiscal Year Company added.
-> Ability to assign multiple companies to a single fiscal year provided.
-> On Changing Posting Date or Company in  Journal Voucher, Sales Invoice, Purchase Invoice, Stock Entry, Purchase Order etc Fiscal year is automatically fetched .
-> User can however change the fetched fiscal year manually.
Why redundant function? Instead pass date fieldname to erpnext.get_fiscal_year()