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/SettingsHandler.js

@@ -0,0 +1,70 @@
+/*
+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';
+
+/**
+ * Represents the base class for all level handlers. This class performs no logic
+ * and should be overridden.
+ */
+export default class SettingsHandler {
+    /**
+     * Gets the value for a particular setting at this level for a particular room.
+     * If no room is applicable, the roomId may be null. The roomId may not be
+     * applicable to this level and may be ignored by the handler.
+     * @param {string} settingName The name of the setting.
+     * @param {String} roomId The room ID to read from, may be null.
+     * @return {Promise<object>} Resolves to the setting value. Rejected if the value
+     * could not be found.
+     */
+    getValue(settingName, roomId) {
+        throw new Error("Operation not possible: getValue was not overridden");
+    }
+
+    /**
+     * Sets the value for a particular setting at this level for a particular room.
+     * If no room is applicable, the roomId may be null. The roomId may not be
+     * applicable to this level and may be ignored by the handler. Setting a value
+     * to null will cause the level to remove the value. The current user should be
+     * able to set the value prior to calling this.
+     * @param {string} settingName The name of the setting to change.
+     * @param {String} roomId The room ID to set the value in, may be null.
+     * @param {Object} newValue The new value for the setting, may be null.
+     * @return {Promise} Resolves when the setting has been saved.
+     */
+    setValue(settingName, roomId, newValue) {
+        throw new Error("Operation not possible: setValue was not overridden");
+    }
+
+    /**
+     * Determines if the current user is able to set the value of the given setting
+     * in the given room at this level.
+     * @param {string} settingName The name of the setting to check.
+     * @param {String} roomId The room ID to check in, may be null
+     * @returns {boolean} True if the setting can be set by the user, false otherwise.
+     */
+    canSetValue(settingName, roomId) {
+        return false;
+    }
+
+    /**
+     * Determines if this level is supported on this device.
+     * @returns {boolean} True if this level is supported on the current device.
+     */
+    isSupported() {
+        return false;
+    }
+}