week-grid, week-view: improve hour sidebar rendering

The hour strings are too soft and can barely be read. Fix
that by setting a stronger color.

https://bugzilla.gnome.org/show_bug.cgi?id=777420

data/theme/gtk-styles.css

@@ -411,11 +411,14 @@ datechooser day:selected:hover {
 
 .week-view .hours {
     font-size: 10pt;
-    font-weight: normal;
-    color: alpha(@theme_fg_color, 0.25);
+    color: alpha(@theme_fg_color, 0.8);
     padding: 8px 12px;
 }
 
+.week-view .lines {
+    color: alpha(@theme_fg_color, 0.30);
+}
+
 weekgrid.now-strip {
     background-color: alpha(@theme_selected_bg_color, 0.8);
     margin: 0 0 0 1px;