[CALC] Add theming support, requires Windows XP or later. CORE-13343

- Fix errors if a theme api is missing.
- Add callback to functions for drawing themed transparent background.
- Fix drawing glitch when theming is applied.
- Redraw on theme change: automatically redraw the window if the
  theme is changed while the application is active.
- Colours are now declared though RGB() macro.
- Removed safe DS_SHELLFONT declaration.

base/applications/calc/CMakeLists.txt

@@ -8,6 +8,7 @@ list(APPEND SOURCE
     utl_ieee.c
     winmain.c
     htmlhelp.c
+    theme.c
     calc.h)
 
 file(GLOB calc_rc_deps res/*.*)