Fiscal year (#5)

* fiscal year feature

* test for fiscal year feature

* removed unwanted files

* stubs Date to pass test for all date

* removes new lines

* - merged with fiscal-year-features

* fix for fetching wrong last date of the given fiscal year and implementation of FiscalYear class

* removed unnessary file and minor changes in fiscal_year

* changes form review

* cleanup

* minor fixes

* FiscalYear object and refactoring

* changes from review

* updates rails version to 6

* rails version to 6.1.0

* changes in fiscal year methods

* few adjustments in specs

* re written test case for FiscalYear

* more test cases for FIscalYear

* BsCalendar object instead of Calendar only

Co-authored-by: sagar535 <070bct535@ioe.edu.np>