gui: simplify blanktimer

- get rid of separate thread, check timer in rendering thread instead
- use an enum for the blanking state instead of magic integers
- move #ifdefs for TW_NO_SCREEN_TIMEOUT inside blanktimer class
- move some #includes and enum TOUCH_STATE to pages.hpp

Change-Id: Id4b104e3680dc5db41d8ba85e32d722cf4086299