Many fixes to ui.taskbar.Icon
Many fixes to ui.taskbar.Icon

- Use wx.Menu derived Menu class.
- Make unnecessary member instances non-members.
- Set state with SetState* methods.
- Rename 'Exit', 'Pause', 'Stop', & 'Record' methods to 'OnExit',
'OnPause', 'OnStop', & 'OnRecord'.
- Update taskbar icon for state.
- Define IsPaused & IsRecording methods.
- Use string to set icon (automatically converts to wx.Icon).
  - Set 'current_icon' member with string (taskbar icon will not be
refreshed if new icon is the same as 'current').
AntumDeluge/desktop_recorder,AntumDeluge/desktop_recorder