Rebuild SettingsStore to be better supported

This does away with the room- and account-style settings, and just replaces them with `supportedLevels`. The handlers have also been moved out to be in better support of the other options, like SdkConfig and per-room-per-device.

Signed-off-by: Travis Ralston <travpc@gmail.com>

src/settings/RoomDeviceSettingsHandler.js

@@ -0,0 +1,52 @@
+/*
+Copyright 2017 Travis Ralston
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import Promise from 'bluebird';
+import SettingsHandler from "./SettingsHandler";
+
+/**
+ * Gets and sets settings at the "room-device" level for the current device in a particular
+ * room.
+ */
+export default class RoomDeviceSettingsHandler extends SettingsHandler {
+    getValue(settingName, roomId) {
+        const value = localStorage.getItem(this._getKey(settingName, roomId));
+        if (!value) return Promise.reject();
+        return Promise.resolve(value);
+    }
+
+    setValue(settingName, roomId, newValue) {
+        if (newValue === null) {
+            localStorage.removeItem(this._getKey(settingName, roomId));
+        } else {
+            localStorage.setItem(this._getKey(settingName, roomId), newValue);
+        }
+
+        return Promise.resolve();
+    }
+
+    canSetValue(settingName, roomId) {
+        return true; // It's their device, so they should be able to
+    }
+
+    isSupported() {
+        return !!localStorage;
+    }
+
+    _getKey(settingName, roomId) {
+        return "mx_setting_" + settingName + "_" + roomId;
+    }
+}