use SerializableUIOptionBase for all options.

[kianzarrin]

there are still some UI options that are not using the SerializableUIOptionBase . Specially drop downs that use Enums.
For more flexibility all options should use SerializableUIOptionBase .

[kianzarrin]

@aubergine10 Also noticed 2 drop-downs not yet converted in GeneralTab_LocalisationGroup.cs:

• language
• road sign theme

I did some investigation on how to do this in https://github.com/CitiesSkylinesMods/TMPE/tree/DropDownOption2
But I realised that its not worth doing it because:

• it is not help Allow main menu to set options for new games #363
• drop down items use different translator than label
• global options have no need of the ILegacySerializableOption.Load()/Save() stuff
• The code in GeneralTab_LocalisationGroup does not get simplified at all.

[krzychu124]

Hot-reload stopped working... (this._ui is null)

Stacktrace

NullReferenceException: Object reference not set to an instance of an object
  at TrafficManager.UI.Helpers.DropDownOption`1[TrafficManager.API.Traffic.Enums.SimulationAccuracy].set_Value (SimulationAccuracy value) [0x00000] in <filename unknown>:0 
  at TrafficManager.UI.Helpers.DropDownOption`1[TrafficManager.API.Traffic.Enums.SimulationAccuracy].Load (Byte data) [0x00000] in <filename unknown>:0 
  at TrafficManager.Manager.Impl.OptionsManager.ToDropDown[SimulationAccuracy] (System.Byte[] data, UInt32 idx, ILegacySerializableOption opt, SimulationAccuracy defaultVal) [0x00000] in <filename unknown>:0 
  at TrafficManager.Manager.Impl.OptionsManager.LoadData (System.Byte[] data) [0x00000] in <filename unknown>:0 
UnityEngine.DebugLogHandler:Internal_LogException(Exception, Object)
UnityEngine.DebugLogHandler:LogException(Exception, Object)
UnityEngine.Logger:LogException(Exception, Object)
UnityEngine.Debug:LogException(Exception)
TrafficManager.Util.Shortcuts:LogException(Exception, Boolean)
TrafficManager.Manager.Impl.OptionsManager:LoadData(Byte[])
TrafficManager.Lifecycle.SerializableDataExtension:Load()
TrafficManager.Lifecycle.TMPELifecycle:Awake()
UnityEngine.GameObject:Internal_AddComponentWithType(Type)
UnityEngine.GameObject:AddComponent(Type)
UnityEngine.GameObject:.ctor(String, Type[])
TrafficManager.Lifecycle.TMPELifecycle:StartMod()
TrafficManager.Lifecycle.TrafficManagerMod:OnEnabled()
System.Reflection.MonoMethod:InternalInvoke(Object, Object[], Exception&)
System.Reflection.MonoMethod:Invoke(Object, BindingFlags, Binder, Object[], CultureInfo)
System.Reflection.MethodBase:Invoke(Object, Object[])
ColossalFramework.Plugins.PluginManager:AddPlugins(Dictionary`2)
ColossalFramework.Plugins.PluginManager:LoadPluginAtPath(String, Boolean, PublishedFileId)
ColossalFramework.Plugins.PluginManager:OnPluginAdded(String)
ColossalFramework.Plugins.<>c__DisplayClass20:<OnFileWatcherEventChanged>b__1a()
ColossalFramework.Threading.<>c__DisplayClass4:<CreateSafeAction>b__3()
ColossalFramework.Threading.<>c__DisplayClassa:<.ctor>b__8(Task)
ColossalFramework.Threading.Task`1:Execute()
ColossalFramework.Threading.Task:InternalExecute()
ColossalFramework.Threading.Dispatcher:RunTask(Task)
ColossalFramework.Threading.Dispatcher:ProcessSingleTask(Task)
ColossalFramework.Threading.Dispatcher:InternalProcessTasks()
ColossalFramework.Threading.Dispatcher:ProcessTasks()

[kianzarrin]

ill put a guard