Bump API version to 3

- New stock item history tracking is incompatible
- Adds API info to the "about" dialog

InvenTree/part/templatetags/inventree_extras.py

@@ -119,6 +119,12 @@ def inventree_version(*args, **kwargs):
     return version.inventreeVersion()
 
 
+@register.simple_tag()
+def inventree_api_version(*args, **kwargs):
+    """ Return InvenTree API version """
+    return version.inventreeApiVersion()
+
+
 @register.simple_tag()
 def django_version(*args, **kwargs):
     """ Return Django version string """