Currency migrations - stop migrations when defaults change (#4975)

* make currency choices independend

* replace hard coded default currency

* use function for psql?

* use callable default

* revert some fields

* also migrat all currency codes

InvenTree/common/settings.py

@@ -23,6 +23,11 @@ def currency_code_default():
     return code
 
 
+def all_currency_codes():
+    """Returns a list of all currency codes."""
+    return [(a, CURRENCIES[a].name) for a in CURRENCIES]
+
+
 def currency_code_mappings():
     """Returns the current currency choices."""
     return [(a, CURRENCIES[a].name) for a in settings.CURRENCIES]