Add preferences option to enable or disable the custom fiscal year handling.

Stored in DB as 0 or 1 and converted:-
- twig expression in view (expandedform needs true boolean)
- checkbox true/false converted to integer in set function in controller

Oh and I worked out how to localize the label ... took me a while but ended up so simple.

This is stage 1 of the overall custom fiscal year extension for Firefly.

resources/lang/en_US/firefly.php

@@ -169,6 +169,9 @@ return [
     'pref_6M'                                => 'Six months',
     'pref_languages'                         => 'Languages',
     'pref_languages_help'                    => 'Firefly III supports several languages. Which one do you prefer?',
+    'pref_custom_fiscal_year'                => 'Fiscal year settings',
+    'pref_custom_fiscal_year_label'          => 'Enabled',
+    'pref_custom_fiscal_year_help'           => 'In countries that use a financial year other than January 1 to December 31, you can switch this on and specify start / end days of the fiscal year',
     'pref_save_settings'                     => 'Save settings',
 
     // profile: