sphinx: Use the pip installed sphinx-rtd-theme

- Remove the RTEMS version of the theme

- Use conf.py to specify our style sheet

- Depend on the jQuery contrib package for including jQuery

- Detect the theme is installed

Closes #4994

common/conf.py

@@ -9,6 +9,7 @@ extensions = [
 	"sphinx.ext.intersphinx",
 	"sphinx.ext.mathjax",
 	"sphinxcontrib.bibtex",
+	"sphinxcontrib.jquery",
 	"rtemsdomain",
 ]
 
@@ -84,9 +85,9 @@ numfig = True
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 
-import sphinx_rtd_theme_rtems
-html_theme = "sphinx_rtd_theme_rtems"
-html_theme_path = [sphinx_rtd_theme_rtems.get_html_theme_path()]
+import sphinx_rtd_theme
+html_theme = "sphinx_rtd_theme"
+html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
 # 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
@@ -122,6 +123,12 @@ html_theme_options = {
 # so a file named "default.css" will overwrite the builtin "default.css".
 html_static_path = ['build/_static']
 
+# These paths are either relative to html_static_path
+# or fully qualified paths (eg. https://...)
+html_css_files = [
+    'my-styles.css',
+]
+
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
 #html_last_updated_fmt = '%b %d, %Y'