add plot.title.position to all themes, add visual test.

Author: clauswilke

R/theme-defaults.r

@@ -488,6 +488,7 @@ theme_void <- function(base_size = 11, base_family = "",
                            hjust = 0, vjust = 1,
                            margin = margin(t = half_line)
                          ),
+    plot.title.position = "panel",
     plot.subtitle =      element_text(
                            hjust = 0, vjust = 1,
                            margin = margin(t = half_line)
@@ -616,6 +617,7 @@ theme_test <- function(base_size = 11, base_family = "",
                            hjust = 0, vjust = 1,
                            margin = margin(b = half_line)
                          ),
+    plot.title.position = "panel",
     plot.subtitle =      element_text(
                            hjust = 0, vjust = 1,
                            margin = margin(b = half_line)