Move get_colorpixel to libi3, use it everywhere else

include/libi3.h

@@ -93,4 +93,20 @@ int ipc_recv_message(int sockfd, uint32_t message_type,
  */
 void fake_configure_notify(xcb_connection_t *conn, xcb_rectangle_t r, xcb_window_t window, int border_width);
 
+/**
+ * Returns the colorpixel to use for the given hex color (think of HTML). Only
+ * works for true-color (vast majority of cases) at the moment, avoiding a
+ * roundtrip to X11.
+ *
+ * The hex_color has to start with #, for example #FF00FF.
+ *
+ * NOTE that get_colorpixel() does _NOT_ check the given color code for validity.
+ * This has to be done by the caller.
+ *
+ * NOTE that this function may in the future rely on a global xcb_connection_t
+ * variable called 'conn' to be present.
+ *
+ */
+uint32_t get_colorpixel(const char *hex) __attribute__((const));
+
 #endif