refactor: params.toml changes for improved theme system

Rename `color_theme` to `theme`.
Default theme has been renamed from Default to Minimal.
The Font set is now set by the theme unless overrided by user in `params.toml`.
Font size is now set in `params.toml` rather than in the font set.
Options for `font_size` are now s,m, or l.

exampleSite/config/_default/params.toml

@@ -1,15 +1,24 @@
 # SITE SETUP
 # Documentation: https://sourcethemes.com/academic/
 
-# Color theme.
-#   Choose from `default`, `ocean`, `forest`, `dark`, `apogee`, `1950s`, `coffee`, `rose`, `strawberry`, `mr_robot`.
-color_theme = "default"
+# Choose a theme.
+#   Latest themes (may require updating Academic): https://sourcethemes.com/academic/themes/
+#   Browse built-in themes in `themes/academic/data/themes/`
+#   Browse user installed themes in `data/themes/`
+theme = "minimal"
+
 # Enable users to switch between day and night mode?
 day_night = true
 
-# Font style.
-#   Choose from `default`, `classic`, `rose`, or `mr_robot`.
-font = "default"
+# Overrride the theme's font set (optional).
+#   Latest font sets (may require updating Academic): https://sourcethemes.com/academic/themes/
+#   Browse built-in font sets in `themes/academic/data/fonts/`
+#   Browse user installed font sets in `data/fonts/`
+font = ""
+
+# Choose a font size.
+# Sizes: s (small), m (medium), l (large)
+font_size = "m"
 
 # Description for social sharing and search engines. If undefined, superuser role is used in place.
 description = ""
@@ -17,10 +26,10 @@ description = ""
 # Default image for social sharing and search engines. Place image in `static/img/` folder and specify image name here.
 sharing_image = ""
 
-# Twitter username (without @). Used when a vistor shares your site on Twitter.
+# Twitter username (without @). Used when a visitor shares your site on Twitter.
 twitter = ""
 
-# Diplay a logo in navigation bar rather than title (optional).
+# Display a logo in navigation bar rather than title (optional).
 #   To enable, place an image in `static/img/` and reference its filename below. To disable, set the value to "".
 logo = ""