Move helpers to external file
Move helpers.rb to helpers/application_helpers.rb
Add basic spec for TimesheetExhibit
Add basic spec for exhibit helper
Simplify exhibit spec using a stub_const 'Timesheet' instead of a class
Clean timesheet_exhibit_spec.rb
Complete spec for helper 'exhibit' with support for Fact objects
Make fact_exhibit support option format: 'default'
Add fact_exhibit spec
Cleanup exhibit helper spec in application_helpers_spec.rb