#40: Add UserSessionStoreProtocol.

Only log out of the specific account.
Add tests for the keychain controller.
Expand test coverage.
PR comments

ElementX/Sources/Other/Extensions/String.swift

@@ -0,0 +1,34 @@
+// 
+// Copyright 2021 New Vector Ltd
+//
+// 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 SwiftUI
+
+extension String {
+    /// Returns the string as an `AttributedString` with the specified character tinted in a different color.
+    /// - Parameters:
+    ///   - character: The character to be tinted.
+    ///   - color: The color to tint the character. Defaults to the accent color.
+    /// - Returns: An `AttributedString`.
+    func tinting(_ character: Character, color: Color = .accentColor) -> AttributedString {
+        var string = AttributedString(self)
+        let characterView = string.characters
+        for index in characterView.indices where characterView[index] == character {
+            string[index..<characterView.index(after: index)].foregroundColor = color
+        }
+        
+        return string
+    }
+}