Revert to default sphinx theme

Remove dependency on EllisLab corporate theme - that is not appropriate for us.
Reverted to default Sphinx theme, with a couple of options, which have the side-effect of adding back document tree navigation (next/previous) and collapsible menu (albeit a sidebar not a top one).

Closes #2605 and closes #2354, for now.
This is not a proper styling - that is a separate issue!
Signed-off-by:James L Parry <jim_parry@bcit.ca>
diff --git a/user_guide_src/source/conf.py b/user_guide_src/source/conf.py
index 118b2fb..5089cf5 100644
--- a/user_guide_src/source/conf.py
+++ b/user_guide_src/source/conf.py
@@ -92,12 +92,22 @@
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
-html_theme = 'eldocs'
+#
+# Reverting to default sphinx theme, to remove dependency on EllisLab corporate style
+#html_theme = 'eldocs'
+html_theme = 'default'
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.
-#html_theme_options = {}
+#
+# Specifying a few options; just a starting point & we can play with it.
+html_theme_options = {
+   "collapsiblesidebar" : "true",
+   "sidebarbgcolor" : "#4b7eb0",
+   "codebgcolor": "#fffded",
+   "headbgcolor": "#ffeebd"
+}
 
 # Add any paths that contain custom themes here, relative to this directory.
 html_theme_path = ["./_themes"]
@@ -116,7 +126,7 @@
 # The name of an image file (within the static path) to use as favicon of the
 # docs.  This file should be a Windows icon file (.ico) being 16x16 or 32x32
 # pixels large.
-#html_favicon = None
+html_favicon = 'images/ci-icon.ico'
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,