Sort categories/pages on the whole name not just the first letter.

Performing a sort only on the first letter doesn't alphabetise the
contents within a given letter section, however sorting on the whole
word will still produce an alphabetised list as a whole.
Refs #9664

Code/Mantid/docs/sphinxext/mantiddoc/directives/categories.py

@@ -264,8 +264,8 @@ def create_category_pages(app):
         context = {}
         context["title"] = category.name
         # sort subcategories & pages by first letter
-        context["subcategories"] = sorted(category.subcategories, key = lambda x: x.name[0])
-        context["pages"] = sorted(category.pages, key = lambda x: x.name[0])
+        context["subcategories"] = sorted(category.subcategories, key = lambda x: x.name)
+        context["pages"] = sorted(category.pages, key = lambda x: x.name)
 
         outdir = CATEGORIES_DIR + "/"
         yield (outdir + name, context, template)