PLT-2992 Added the ability to use different themes for each team (#3411)

* Cleaned up user_settings_theme.jsx and import_theme_modal.jsx

* Made ImportThemeModal use a callback to return the theme to the user settings modal instead of saving it directly

* Moved user theme from model to preferences

* Added serverside API to delete preferences TODO update package with client stuff

* Changed constants.jsx so that Preferences and ActionTypes can be imported on their own

* Updated ThemeProps migration code to properly rename solarized code themes

* Fixed warnings thrown by AppDispatcher

* Added clientside UI to support team-specific themes

* Removed debugging code from test

* Fixed setting a user's theme when they haven't set their theme before

webapp/utils/async_client.jsx

@@ -852,6 +852,29 @@ export function savePreferences(preferences, success, error) {
     );
 }
 
+export function deletePreferences(preferences, success, error) {
+    Client.deletePreferences(
+        preferences,
+        (data) => {
+            AppDispatcher.handleServerAction({
+                type: ActionTypes.DELETED_PREFERENCES,
+                preferences
+            });
+
+            if (success) {
+                success(data);
+            }
+        },
+        (err) => {
+            dispatchError(err, 'deletePreferences');
+
+            if (error) {
+                error();
+            }
+        }
+    );
+}
+
 export function getSuggestedCommands(command, suggestionId, component) {
     Client.listCommands(
         (data) => {