feat: add configurable hotkeys to cycle tabs

Adds two configurable hotkeys (plus the required code infrastructure to
handle configurable hotkeys) for cycling the active chat tab forward by
one and backwards by one.

ChatTwo/GameFunctions/Types/ModifierFlag.cs

@@ -3,6 +3,7 @@ namespace ChatTwo.GameFunctions.Types;
 [Flags]
 internal enum ModifierFlag
 {
+    None = 0,
     Shift = 1 << 0,
     Ctrl = 1 << 1,
     Alt = 1 << 2,