Provide global_settings and user_settings as context objects

- Adds a new context middleware
- Refactor the way that settings are provided to the javascript layer

InvenTree/templates/js/dynamic/settings.js

@@ -1,17 +1,14 @@
 {% load inventree_extras %}
 // InvenTree settings
 
-{% user_settings request.user as USER_SETTINGS %}
-{% global_settings as GLOBAL_SETTINGS %}
-
 var user_settings = {
-    {% for setting in USER_SETTINGS %}
-    {{ setting.key }}: {{ setting.value }},
+    {% for key, value in user_settings.items %}
+    {{ key }}: {% primitive_to_javascript value %},
     {% endfor %}
 };
 
 var global_settings = {
-    {% for setting in GLOBAL_SETTINGS %}
-    {{ setting.key }}: {{ setting.value }},
+    {% for key, value in global_settings.items %}
+    {{ key }}: {% primitive_to_javascript value %},
     {% endfor %}
 };