Remove retired theme aliases (#430)

* Remove required theme aliases

Replaced uses of headerURL, accentcolor, and textcolor with theme_frame, frame, and tab_background_text. Tested and confirmed all extensions working as expected.

* Fixed another reference to headerURL

Co-authored-by: Richard Bloor <rbloor@atlassian.com>

dynamic-theme/background.js

@@ -3,20 +3,20 @@ var currentTheme = '';
 const themes = {
   'day': {
     images: {
-      headerURL: 'sun.jpg',
+      theme_frame: 'sun.jpg',
     },
     colors: {
-      accentcolor: '#CF723F',
-      textcolor: '#111',
+      frame: '#CF723F',
+      tab_background_text: '#111',
     }
   },
   'night': {
     images: {
-      headerURL: 'moon.jpg',
+      theme_frame: 'moon.jpg',
     },
     colors: {
-      accentcolor: '#000',
-      textcolor: '#fff',
+      frame: '#000',
+      tab_background_text: '#fff',
     }
   }
 };