Use the DPI setting within the i3bar (#2556)

include/libi3.h

@@ -473,6 +473,12 @@ char *get_exe_path(const char *argv0);
  */
 void init_dpi(void);
 
+/**
+ * This function returns the value of the DPI setting.
+ *
+ */
+long get_dpi_value(void);
+
 /**
  * Convert a logical amount of pixels (e.g. 2 pixels on a “standard” 96 DPI
  * screen) to a corresponding amount of physical pixels on a standard or retina