create map preview pictures during spectating

pressing CTRL+F12 during spectating creates a clean screenshot and saves
it as map preview picture

  modkeypressed

    returns 1, if a CTRL key is pressed and 0, if not

  screenshotpreview [lines]

    creates a screenshot cropped to 4:3 with a given number of lines
    (in the range of 144 to 480, default 240 or last given value)
    and jpeg quality 80

  gotovantagepoint

    now returns 1, if the map actually has a vantage point set

DOCREF screenshotpreview modkeypressed gotovantagepoint

source/src/console.cpp

@@ -206,6 +206,8 @@ void findkeycode(const char* s)
 }
 COMMAND(findkeycode, "s");
 
+COMMANDF(modkeypressed, "", () { intret((SDL_GetModState() & MOD_KEYS_CTRL) ? 1 : 0); });
+
 keym *keypressed = NULL;
 char *keyaction = NULL;