Add compact panels support

Add a configuration option that allows for switching to compact panel
mode. In this mode, all window labels are hidden, so that there's more
space for actual information.

This patch doesn't add a configuration menu entry and doesn't add any
documentation.

Implements FR#7.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/vars.c

@@ -135,6 +135,7 @@ void vars_init(void)
   conf.auto_gc = 0;
   conf.periodic_save = 0;
   conf.default_panel = CAL;
+  conf.compact_panels = 0;
   conf.system_dialogs = 1;
   conf.progress_bar = 1;
   strncpy(conf.output_datefmt, "%D", 3);