Add 'About InvenTree' modal

- Accessible from the top-right dropdown menu
- Add InvenTree/version.py which contains helper functions

InvenTree/part/templatetags/inventree_extras.py

@@ -0,0 +1,28 @@
+""" This module provides template tags for extra functionality
+over and above the built-in Django tags.
+"""
+
+from django import template
+from InvenTree import version
+
+register = template.Library()
+
+
+@register.simple_tag()
+def multiply(x, y, *args, **kwargs):
+    return x * y
+
+
+@register.simple_tag()
+def inventree_version(*args, **kwargs):
+    return version.inventreeVersion()
+
+
+@register.simple_tag()
+def inventree_commit(*args, **kwargs):
+    return version.inventreeCommitHash()
+
+
+@register.simple_tag()
+def inventree_github(*args, **kwargs):
+    return "https://github.com/InvenTree"