add width query param option

Closes #1272

lib/routing.js

@@ -60,6 +60,7 @@ const readMappings = [
   { field: 't:theme' },
   { field: 'wt:windowTheme' },
   { field: 'l:language' },
+  { field: 'width' },
   { field: 'ds:dropShadow', type: 'bool' },
   { field: 'dsyoff:dropShadowOffsetY' },
   { field: 'dsblur:dropShadowBlurRadius' },
@@ -88,6 +89,7 @@ const writeMappings = [
   { field: 'theme:t' },
   { field: 'windowTheme:wt' },
   { field: 'language:l' },
+  { field: 'width' },
   { field: 'dropShadow:ds', type: 'bool' },
   { field: 'dropShadowOffsetY:dsyoff' },
   { field: 'dropShadowBlurRadius:dsblur' },