GCHP RTD doc updates for consistency with GEOS-Chem and HEMCO RTD sites

docs/source/conf.py
- Import pybtex alphabetic formatting style as AlphaStyle, which is
  the base class for GcRefStyle.  This will list all of the bibliography
  citations alphabetically by first-author surname.
- Add geos-chem-shared-docs/_static to html_static_path list
- Add html_css_files list
- Now display rectangular GEOS-Chem logo (as GCClassic and HEMCO do)
- Display the title above the logo (as GCClassic and HEMCO do)

docs/source/bibtex.json
- Removed. The version of sphinxcontrib-bibtex that we use (2.2.0) no
  longer requires a JSON file to list the references to be displayed.
  It can figure that out automatically.

docs/source/_static/css/icon_home.css
- Style sheet to change the project name (GCHP) above the GEOS-Chem logo
  from white to black.  This only affects the look of the page on a
  computer desktop web browser but not on a mobile device.

Signed-off-by: Bob Yantosca <yantosca@seas.harvard.edu>

docs/source/_static/css/icon_home.css

@@ -0,0 +1,4 @@
+/* Sets the color of text above the GEOS-Chem logo to black at top left */
+.wy-side-nav-search a {
+    color: black;
+}

docs/source/conf.py

@@ -32,7 +32,7 @@
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
 extensions = [
-    "sphinx_rtd_theme",   
+    "sphinx_rtd_theme",
     "sphinxcontrib.bibtex",
     "recommonmark",
 ]
@@ -50,9 +50,7 @@ def format_labels(self, sorted_entries):
             yield entry.key.replace("_", " ").replace("et al.", "et al.,")
 
 class GCRefStyle(AlphaStyle):
-    # Using pybtex.style.formatting.alpha will list citations
-    # in alphabetical order by last author name, then by year.
-    #  -- Bob Yantosca (30 Jun 2022)
+    # Sorts authors alphabetically by last name
     default_name_style = LastFirst
     default_sort_style = None
     default_label_style = GCLabelStyle
@@ -95,14 +93,25 @@ def format_web_refs(self, e):
 # 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,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+html_static_path = [
+    '_static',
+    'geos-chem-shared-docs/_static/',
+]
 
+# CSS files that will override sphinx-rtd-theme default settings
+# (paths are relative to _static, which is specified above)
+html_css_files = [
+    'css/icon_home.css',
+    'theme_overrides.css',
+]
 
-# Display GEOS-Chem logo
+# Display GEOS-Chem favicon and logo
 html_favicon = 'geos-chem-shared-docs/_static/gc-o-logo-favicon.ico'
-html_logo = "geos-chem-shared-docs/_static/geos-chem-logo.svg"
+html_logo = "geos-chem-shared-docs/_static/GEOS-Chem_Logo_Light_Background.png"
+
+# More theme settings
 html_theme_options = {
-    'logo_only': True,
-    'display_version': False,
-    'style_nav_header_background': '#FCFCFC',
+    'logo_only': False,                        # Show logo & top text
+    'display_version': False,                  # Don't show version number
+    'style_nav_header_background': '#FCFCFC',  # 99% white for top left bkgrnd
 }